Shoulder dystocia is an obstetric emergency in which, after delivery of the fetal head, one or both fetal shoulders become impacted behind the maternal pubic symphysis, requiring additional maneuvers beyond gentle downward traction to complete delivery.

Exam domain	One-glance essentials
Definition / diagnosis	*Shoulder dystocia is failure of the shoulders to deliver with gentle axial traction after the fetal head, requiring additional manoeuvres* ^[1]^[2] It is an unpredictable obstetric emergency caused most often by anterior-shoulder impaction behind the pubic symphysis ^[1]
Epidemiology / risks	Risk factors include previous shoulder dystocia, fetal macrosomia, diabetes, maternal obesity, prolonged labour, and operative vaginal birth ^[1]^[2] Risk factors predict poorly and many cases occur without them ^[1]
Core mechanism	The bisacromial diameter becomes impacted in the maternal pelvis → cord compression and delayed body delivery → fetal hypoxia ^[1] Traction against an impacted shoulder can injure the brachial plexus or fracture bone ^[2]
Clinical picture	*The turtle sign, failure of restitution, and failure of the shoulders to descend with routine traction are classic* ^[1]^[2] Announce the emergency and record the head-to-body interval while avoiding forceful traction ^[1]
Investigations	Diagnosis is clinical during birth; there is no time for confirmatory testing ^[1] After delivery assess the neonate for brachial plexus injury, fractures, and hypoxic injury, and the mother for haemorrhage or genital trauma ^[1]^[2]
Management	*Call for help, stop pushing, use McRoberts manoeuvre and suprapubic pressure, then systematic internal manoeuvres or posterior-arm delivery* ^[1]^[2] Avoid fundal pressure and excessive downward traction; use last-resort rescue procedures only with senior expertise ^[1]
Complications	Fetal complications include brachial plexus injury, clavicle or humerus fracture, hypoxia, and death ^[1]^[2] Maternal complications include PPH, third- or fourth-degree tears, uterine rupture, and psychological trauma ^[1]
Prevention / follow-up	Optimise diabetes and discuss birth planning when prior dystocia or suspected extreme macrosomia raises risk, while acknowledging imperfect prediction ^[1]^[2] Regular multidisciplinary drills, clear role allocation, and accurate documentation improve emergency response ^[1]
Exam traps	*Fundal pressure worsens impaction and must not be used* ^[1]^[2] An episiotomy does not release the bony obstruction; it only creates room for internal manoeuvres when needed ^[1]

References

^[1] Lecture slides: Block C - Obstetric Emergency Notes to Students.pdf (shoulder dystocia recognition and manoeuvres) ^[2] Lecture slides: OBGYN Clinical Test By Topic.pdf (shoulder dystocia exam points and complications)

Shoulder Dystocia

Shoulder dystocia is defined as a delivery that requires additional obstetric manoeuvres to release the shoulders after gentle downward traction has failed, or when there is a head-to-body delivery interval of > 60 seconds. ^[1]^[2]

Breaking down the term:

"Shoulder" = the fetal shoulders (specifically the anterior shoulder)
"Dystocia" → from Greek dys- (difficult) + tokos (birth/labour) = difficult birth

The core mechanical problem: after the fetal head delivers, the anterior shoulder becomes impacted behind the maternal pubic symphysis. The fetus is essentially "stuck" at the level of the bony pelvic inlet. This is a true obstetric emergency — the clock starts ticking because the umbilical cord is being compressed between the fetal body and the bony pelvis, and the delivered head cannot ventilate while the thorax remains compressed in the birth canal.

Key Distinction

Shoulder dystocia is NOT simply a "tight" delivery. It is defined by the need for additional manoeuvres beyond routine axial traction. A delivery where the shoulders come with a bit of extra effort but no special manoeuvres is called a "tight shoulder" — not shoulder dystocia. This distinction matters for documentation, audit, and medicolegal purposes.

Incidence: approximately 0.6–1.4% of all vaginal cephalic deliveries ^[1]^[2]. Some studies cite up to 2% depending on the definition used.
The incidence is rising in many countries, attributed to:
- Increasing maternal obesity
- Rising rates of gestational diabetes mellitus (GDM) — particularly relevant in Hong Kong where GDM prevalence is approximately 15–20% ^[3]
- Increasing average birth weight
Recurrence risk: women with a prior shoulder dystocia have a recurrence risk of approximately 1–25% (commonly quoted as ~10–15%) in subsequent deliveries ^[1]^[2]
Hong Kong context: Given the relatively high prevalence of GDM among Hong Kong Chinese women and increasing trends in maternal obesity, shoulder dystocia remains a significant concern despite the generally smaller average birth weight compared to Western populations. However, macrosomia relative to maternal pelvic size (i.e., feto-pelvic disproportion) is what matters, not absolute birth weight alone.

3. Anatomy & Function

Understanding shoulder dystocia requires understanding the bony pelvis and its diameters:

Pelvic Plane	Anteroposterior (AP) Diameter	Transverse Diameter	Key Feature
Pelvic inlet	~11 cm (obstetric conjugate)	~13 cm	Widest diameter is transverse
Mid-pelvis	~12 cm	~10.5 cm	Narrowest transverse (ischial spines)
Pelvic outlet	~9.5–11.5 cm	~11 cm (intertuberous)	AP increases with sacral mobility

Normal mechanism of delivery of the shoulders:

After the head delivers and restitutes, the bisacromial diameter (shoulder width, normally ~12 cm) enters the pelvic inlet in an oblique diameter
The anterior shoulder descends behind the pubic symphysis
With gentle downward traction, the anterior shoulder slides under the symphysis pubis
The posterior shoulder follows by flexing over the perineum

In shoulder dystocia:

The bisacromial diameter attempts to enter the pelvis in the AP diameter of the inlet (which is the shorter diameter at the inlet level — only ~11 cm)
The anterior shoulder impacts on the pubic symphysis and cannot descend into the pelvis
Sometimes BOTH shoulders are above the pelvic inlet (bilateral shoulder dystocia — the worst scenario)
The "turtle sign" occurs: after the head delivers, it retracts back against the perineum (the neck is pulled back because the shoulders cannot follow)

The bisacromial diameter is the critical fetal measurement — normally ~12 cm at term but can be ≥14 cm in macrosomic infants ^[1]
In diabetic macrosomia, there is disproportionate growth of the trunk and shoulders relative to the head (due to fetal hyperinsulinism causing glycogen/fat deposition predominantly in the trunk). This is why diabetic macrosomia carries a higher risk of shoulder dystocia than constitutional macrosomia of the same weight.
The brachial plexus (C5–T1) runs from the neck through the axilla — it is stretched during shoulder dystocia when traction is applied to the head while the shoulder is stuck, leading to brachial plexus injury

C5 ──┐
C6 ──┤── Upper trunk → Erb-Duchenne palsy (C5-C6)
     │
C7 ──┤── Middle trunk
     │
C8 ──┤── Lower trunk → Klumpke palsy (C8-T1)
T1 ──┘

Erb-Duchenne palsy (C5–C6): "Waiter's tip" position — arm adducted, internally rotated, elbow extended, forearm pronated, wrist flexed. This is the most common brachial plexus injury in shoulder dystocia (~80%)
Klumpke palsy (C8–T1): Claw hand — rare in isolation, occurs with excessive upward traction
Total plexus palsy (C5–T1): Flail arm — worst prognosis

4. Risk Factors

Exam Pearl – Risk Factors for Shoulder Dystocia

Think of risk factors in two categories: antepartum (before labour) and intrapartum (during labour). However, remember that approximately 50% of shoulder dystocia cases occur with NO identifiable risk factors — this is why ALL birth attendants must be trained in managing it ^[1]^[2].

Risk Factor	Mechanism / Why It Matters
Fetal macrosomia (EFW > 4000g, especially > 4500g) ^[1]^[2]	Larger bisacromial diameter; in diabetic mothers, disproportionate truncal growth makes the shoulder-to-head ratio even larger
Maternal diabetes (pre-existing or gestational) ^[1]^[2]^[3]	Fetal hyperinsulinism → disproportionate fat/glycogen deposition in trunk and shoulders; GDM prevalence is high in HK (~15-20%)
Maternal obesity (BMI > 30) ^[1]	Associated with larger babies, GDM, and soft tissue narrowing of the pelvis
Previous shoulder dystocia ^[1]^[2]	Recurrence risk ~10–15%; reflects persistent maternal pelvic anatomy + tendency for similar-sized babies
Post-term pregnancy (> 42 weeks) ^[1]	Continued fetal growth → larger baby
Maternal short stature	Smaller pelvic dimensions relative to fetal size
Advanced maternal age ^[3]	Associated with GDM, macrosomia
Male fetus	Males are on average heavier and have broader shoulders than females at same gestational age
Excessive maternal weight gain in pregnancy	Contributes to fetal macrosomia

Risk Factor	Mechanism / Why It Matters
Prolonged first and/or second stage of labour ^[1]^[2]	Suggests feto-pelvic disproportion; the large shoulders are having difficulty navigating the pelvis
Instrumental (operative vaginal) delivery ^[1]^[2]^[4]	Forceps/vacuum can deliver the head past a pelvis that the shoulders cannot negotiate; removes the natural "self-limiting" mechanism where the head also wouldn't deliver if shoulders truly can't fit
Oxytocin augmentation ^[1]	May force a baby through a pelvis it wouldn't naturally traverse
Precipitous labour	Baby descends so rapidly that the shoulders don't have time to rotate properly

Critical Exam Point

Despite knowing these risk factors, shoulder dystocia CANNOT be reliably predicted or prevented. The sensitivity and positive predictive value of risk factor-based prediction are poor. Even ultrasound estimation of fetal weight has a margin of error of ±10–15%. Therefore, the most important strategy is preparedness and training, not prediction ^[1]^[2].

5. Aetiology & Pathophysiology

In the Hong Kong context, the most relevant aetiological factors are:

Gestational Diabetes Mellitus (GDM): Hong Kong has a high prevalence of GDM (~15–20% by IADPSG criteria). Even with good glycaemic control, some degree of fetal macrosomia may occur. Diabetic macrosomia is disproportionate — the shoulders and trunk grow more than the head due to fetal hyperinsulinism ^[1]^[3]
Changing demographics: Increasing maternal age, increasing BMI, and adoption of Western dietary patterns in HK are contributing to larger babies
Constitutional macrosomia: Large babies from tall/large parents — here the macrosomia tends to be proportionate (head and shoulders both large), so the head is more likely to also encounter difficulty, acting as a "warning"

Why does the anterior shoulder get stuck?

Normally, the shoulders enter the pelvic inlet in an oblique diameter and rotate to AP as they descend
In shoulder dystocia, the shoulders attempt to enter in the AP diameter of the inlet — which is shorter (~11 cm) than the oblique (~12.5 cm)
If the bisacromial diameter > AP diameter of the inlet → impaction
The posterior shoulder may or may not have entered the pelvis:
- If the posterior shoulder is in the pelvis → unilateral impaction (more common, easier to resolve)
- If both shoulders are above the inlet → bilateral impaction (rarer, more difficult)

Why is time critical?

The umbilical cord is compressed between the fetal body and maternal pelvis → cessation of placental gas exchange
The delivered head attempts to breathe but the thorax is compressed → cannot expand lungs
Irreversible brain injury can occur within 4–8 minutes if the shoulders are not delivered
The pH drops approximately 0.04 units per minute during shoulder dystocia

Why does brachial plexus injury occur?

When the clinician applies lateral traction to the fetal head to try to free the anterior shoulder, the neck is stretched on the side of the anterior shoulder
The brachial plexus (C5–T1) is stretched between two fixed points: the cervical spine (held by the vertebral column) and the shoulder (held by the pubic symphysis)
This traction neuropraxia (stretching of the nerve) causes Erb palsy (C5–C6 most commonly)
Importantly, brachial plexus injury can also occur from endogenous forces (maternal pushing/uterine contractions) without any clinician traction — this is an important medicolegal point ^[1]

Complication	Pathophysiology
Brachial plexus injury	Stretch injury to C5–T1 nerve roots during traction (or endogenous forces) with shoulder impacted behind symphysis
Fracture of clavicle/humerus	Direct compression of bone against pubic symphysis, or during delivery manoeuvres (intentional clavicular fracture is sometimes performed)
Fetal hypoxia/asphyxia	Cord compression + inability to ventilate while thorax compressed
Postpartum haemorrhage	Uterine atony from prolonged/difficult delivery; cervical/vaginal lacerations from manoeuvres
3rd/4th degree perineal tears	Manoeuvres may extend episiotomy or cause tears
Maternal psychological trauma	Traumatic birth experience → PTSD, postnatal depression

6. Classification

Type	Description	Frequency
Unilateral	Only the anterior shoulder is impacted behind the symphysis; posterior shoulder has entered the pelvis	More common (~80%)
Bilateral	Both anterior AND posterior shoulders are above the pelvic inlet	Less common (~20%); more difficult to resolve

Category	Features
Recognised shoulder dystocia	Turtle sign observed; head-to-body interval > 60 seconds; additional manoeuvres required
Unrecognised / "Tight shoulders"	Moderate difficulty delivering shoulders but resolved with slightly increased traction (no special manoeuvres) — NOT shoulder dystocia by strict definition

Grade	Description
Mild	Resolved with simple manoeuvres (McRoberts + suprapubic pressure); no fetal injury
Moderate	Required internal manoeuvres; minor fetal injury (transient brachial plexus palsy, clavicular fracture)
Severe	Multiple manoeuvres needed; significant fetal injury (permanent brachial plexus palsy, fractures, hypoxic-ischaemic encephalopathy) or maternal injury
Fatal	Fetal death due to asphyxia

7. Clinical Features

Symptom	Pathophysiological Basis
"Something is stuck" — inability to deliver after the head	The anterior shoulder is mechanically impacted behind the pubic symphysis; normal gentle traction cannot dislodge it
Prolonged head-to-body delivery interval	The shoulders cannot navigate the pelvic inlet → delay > 60 seconds
Maternal distress / pain	The fetal shoulders are pressing against the vaginal tissues and pelvic floor; maternal anxiety from the emergency situation
Difficulty with maternal pushing	Even with maximal maternal expulsive effort, the mechanical obstruction prevents delivery

Sign	Pathophysiological Basis
"Turtle sign" (turtle neck sign) ^[1]^[2]	After the head delivers, it retracts back tightly against the perineum. This occurs because the anterior shoulder is stuck behind the symphysis, pulling the neck (and therefore the head) backwards. The head appears to "pop back in" like a turtle retracting into its shell
Failure of restitution	Normally after head delivery, the head rotates 45° to align with the shoulders (restitution). In shoulder dystocia, the impacted shoulders prevent this rotation
Head bobbing	The head delivers and then retracts with each contraction — the baby's head comes forward with pushing then retracts when the contraction ends
Failure of shoulders to deliver with routine axial (downward) traction	The mechanical impaction means that simple traction in the normal axis cannot overcome the obstruction
Red/purple discolouration of fetal face	Venous congestion — blood flows into the head via the carotid arteries but cannot drain via the jugular veins (compressed between the thorax and pelvis)
Large episiotomy already in situ or need for urgent episiotomy	Soft tissue of the perineum is under extreme tension from the impacted shoulders

The Turtle Sign is the Hallmark

The "turtle sign" is the classic heralding sign of shoulder dystocia. The moment you see the delivered head retract against the perineum, you must immediately call for help and initiate the shoulder dystocia drill. Do NOT apply excessive downward traction — this increases the risk of brachial plexus injury ^[1]^[2].

Sign	What It Indicates
Moro reflex asymmetry / "Waiter's tip" posture in newborn	Erb-Duchenne palsy (C5–C6 brachial plexus injury) — arm adducted, internally rotated, elbow extended, forearm pronated
Claw hand in newborn	Klumpke palsy (C8–T1) — rare
Flail arm	Total brachial plexus palsy (C5–T1)
Crepitus / swelling over clavicle or humerus	Fracture from delivery manoeuvres or compression
Low Apgar scores / poor tone / no cry	Fetal hypoxia/asphyxia from cord compression and inability to ventilate
Postpartum haemorrhage	Uterine atony (from prolonged/traumatic delivery) or genital tract lacerations
Perineal tears	Mechanical trauma from manoeuvres

Clinical Feature	Underlying Mechanism
Turtle sign	Anterior shoulder impacted behind symphysis pulls head back
Failed restitution	Impacted shoulders prevent normal rotation
Facial congestion	Jugular venous obstruction with preserved arterial inflow
Fetal bradycardia	Cord compression → hypoxia → vagal reflex
Erb palsy	Lateral neck traction stretches C5–C6 roots between fixed spine and impacted shoulder
Clavicular fracture	Bone compressed between shoulder and pubic symphysis
PPH	Uterine atony from prolonged labour + genital tract trauma
Perineal tears	Mechanical trauma from urgent manoeuvres in a tight space

High Yield Summary

Shoulder Dystocia — Key Points for Exams

Definition: Need for additional obstetric manoeuvres after gentle downward traction fails to deliver the shoulders, OR head-to-body interval > 60 seconds
Incidence: ~0.6–1.4% of vaginal cephalic deliveries
Mechanism: Anterior shoulder impacted behind pubic symphysis; bisacromial diameter > AP diameter of pelvic inlet
Risk factors: Fetal macrosomia (especially diabetic macrosomia), GDM, maternal obesity, previous shoulder dystocia, prolonged labour, instrumental delivery — but ~50% are UNPREDICTABLE
Key sign: Turtle sign — head delivers then retracts against the perineum
Time-critical: Irreversible brain injury within 4–8 minutes; cord pH drops ~0.04/min
Diabetic vs constitutional macrosomia: Diabetic macrosomia is DISPROPORTIONATE (trunk > head) → higher risk of shoulder dystocia at any given weight
Brachial plexus injury: Most commonly Erb palsy (C5–C6); can occur from clinician traction OR endogenous forces
Cannot be reliably predicted or prevented → ALL birth attendants must be trained in management drills

Active Recall - Shoulder Dystocia (Definition, Epidemiology, Risk Factors, Anatomy, Pathophysiology, Clinical Features)

^[1] Lecture slides: Block C - Obstetric Emergency Notes to Students.pdf ^[2] Lecture slides: OBGYN Clinical Test By Topic.pdf ^[3] Lecture slides: GC 224. Hypertension and Pregnancy.pdf (predisposing factors including DM) ^[4] Senior notes: Maksim Medicine Notes.pdf; Ryan Ho GI.pdf (general principles referenced for maternal pelvic floor context)

Differential Diagnosis of Shoulder Dystocia

At first glance, shoulder dystocia seems straightforward — the head is out, the shoulders are stuck. But the critical clinical question at the moment of delivery is: "Is this truly shoulder dystocia, or is there another reason the baby isn't delivering after the head?" Misdiagnosis wastes precious seconds and may lead to inappropriate manoeuvres. Additionally, understanding the differential helps you recognise conditions that mimic or co-exist with shoulder dystocia, and conditions that predispose to it but present with overlapping clinical pictures during labour.

Be systematic in problem solving:

What is the probability diagnosis?
What serious disorders cannot be missed (red flags)?
What conditions are often missed (pitfalls)?
Could this patient have a 'masquerade'?
Is this patient trying to tell me something else (hidden agenda)? ^[5]

Let us apply this framework to the scenario of failure of shoulder delivery after the fetal head has been born:

Murtagh's Framework	Application to Shoulder Dystocia
Probability diagnosis	True shoulder dystocia (anterior shoulder impacted behind pubic symphysis)
Serious disorders not to miss	Bilateral shoulder dystocia; locked twins; congenital fetal anomaly causing obstruction; cord around body
Often missed (pitfalls)	"Tight shoulders" mistaken for dystocia (or vice versa); posterior shoulder dystocia; body dystocia
Masquerade	Short umbilical cord preventing delivery; cervical entrapment of a second twin
Hidden agenda	Inadequate anticipation despite known risk factors; medicolegal documentation issues

When the fetal head has delivered but the body does not follow, consider the following differential diagnoses:

Diagnosis	Key Differentiating Features	Mechanism / Why It Mimics Shoulder Dystocia
1. True anterior shoulder dystocia (most common)	Turtle sign present; head retracts against perineum; gentle downward traction fails ^[1]^[2]	Anterior shoulder impacted behind the pubic symphysis; bisacromial diameter exceeds AP diameter of pelvic inlet
2. "Tight shoulders" (difficult shoulder delivery)	Shoulders deliver with slightly increased traction; no special manoeuvres needed; head-to-body interval < 60 sec	Mild degree of shoulder snugness at the pelvic inlet but not true mechanical impaction; the shoulder slips under the symphysis with gentle repositioning. This is NOT shoulder dystocia by definition — the distinction matters for documentation and audit
3. Posterior shoulder dystocia	Head delivers but turtle sign may be less pronounced; the posterior shoulder is impacted on the sacral promontory rather than the anterior on the symphysis	Much rarer; the posterior shoulder catches on the sacral promontory. Standard suprapubic pressure may be ineffective because it targets the wrong shoulder. Requires internal manoeuvres directed at the posterior shoulder
4. Bilateral shoulder impaction	Both shoulders above the pelvic inlet; extremely resistant to all first-line manoeuvres (McRoberts, suprapubic pressure)	Both the anterior and posterior shoulders cannot enter the pelvis. Most severe form. May require last-resort manoeuvres (Zavanelli or symphysiotomy)
5. Short umbilical cord	Head delivers but body doesn't advance; no turtle sign; the head does not retract — instead you may feel resistance when gently pulling the baby, as if tethered	An abnormally short cord (< 35 cm, or a normal cord wrapped tightly around the body/neck multiple times creating a functionally short cord) physically prevents the baby from descending further. The shoulders are NOT impacted behind bone — the tethering is from below. Management: clamp and cut the cord if accessible
6. Cord around the neck/body (nuchal cord / body cord)	May see or palpate cord loops around the neck after head delivery; multiple tight loops can mimic shoulder dystocia by preventing descent	The cord acts as a noose or tether. A loose nuchal cord can be slipped over the head. A tight or multiple-loop cord may need to be clamped and cut before the body can deliver
7. Congenital fetal anomaly	May have abnormal antenatal scans; the obstruction pattern may be unusual (e.g., enlarged abdomen rather than broad shoulders)	Fetal conditions causing massive abdominal distension (e.g., severe hydrops fetalis, massive ascites, abdominal tumours such as sacrococcygeal teratoma, conjoined twins) can cause obstruction that presents similarly to shoulder dystocia but at a different anatomical level
8. Locked twins	Only occurs in twin deliveries; first twin is breech, second is cephalic; chins interlock	The second twin's head descends alongside the first twin's aftercoming head, and the two become interlocked. The scenario is different from singleton shoulder dystocia but produces a similar "can't deliver the body" picture
9. Cervical constriction ring (Bandl's ring equivalent at cervix)	Prolonged second stage; cervix may have contracted around the fetal neck after the head delivered; rarely occurs	A localised tetanic contraction of the lower uterine segment/cervix grips the fetal neck. The body cannot pass through the tonic ring. Requires tocolysis (e.g., GTN, terbutaline) to relax the ring, not shoulder dystocia manoeuvres
10. Body dystocia	Shoulders deliver but the trunk/abdomen is stuck	Massive fetal abdominal distension (hydrops, tumour, organomegaly) causes obstruction at the level of the fetal abdomen, not the shoulders. This is extremely rare

The following diagram shows the thought process at the critical moment when the head has delivered but the body does not follow:

Key Differentiating Points: True Shoulder Dystocia vs Mimics

Feature	True Shoulder Dystocia	Tight Shoulders
Turtle sign	Present	Absent or minimal
Head-to-body interval	> 60 seconds	< 60 seconds
Additional manoeuvres needed	Yes (McRoberts, suprapubic pressure, internal rotation, etc.)	No — resolves with slightly increased routine traction
Risk of brachial plexus injury	Significant	Minimal
Documentation	Must be recorded as shoulder dystocia	Recorded as normal vaginal delivery

Common Exam Mistake

Students often conflate "tight shoulders" with shoulder dystocia. Remember: the defining criterion is the need for additional obstetric manoeuvres beyond gentle downward traction. If you only needed a bit more pull and no special manoeuvres, it is NOT shoulder dystocia. This distinction is critical for medicolegal documentation, audit, and future pregnancy counselling (recurrence risk only applies if it was true shoulder dystocia).

Feature	Shoulder Dystocia	Short/Nuchal Cord
Turtle sign	Classic — head retracts due to shoulder impaction	May not retract in the same way; head may stay extended but body won't advance
Palpation of cord	Cord not the issue	Cord loops palpable around the neck or body
Response to McRoberts	May resolve	Will NOT resolve — the problem is cord tethering, not bony impaction
Management	Shoulder dystocia drill	Clamp and cut the cord, then deliver normally

Feature	Anterior Shoulder Dystocia	Posterior Shoulder Dystocia
Site of impaction	Anterior shoulder behind pubic symphysis	Posterior shoulder on sacral promontory
Frequency	Much more common	Rare
Suprapubic pressure	May be effective (pushes anterior shoulder off symphysis)	Ineffective (wrong shoulder)
Internal manoeuvres	Deliver posterior arm or internal rotation	Same manoeuvres but directed at the posterior shoulder specifically

After a shoulder dystocia event, you must consider why it occurred, both for the current management and for future pregnancy counselling:

Predisposing Condition	How It Leads to Shoulder Dystocia
Gestational diabetes mellitus ^[1]^[3]	Fetal hyperinsulinism → disproportionate truncal fat/glycogen deposition → bisacromial diameter > head circumference ratio is increased
Fetal macrosomia (> 4000g, especially > 4500g) ^[1]^[2]	Absolutely larger shoulders that exceed the pelvic inlet dimensions
Maternal obesity ^[1]	Larger babies + soft tissue narrowing of pelvis + higher GDM rates
Prolonged second stage of labour ^[1]^[2]	Suggests feto-pelvic disproportion — the large shoulders are struggling to navigate
Instrumental delivery (forceps/vacuum) ^[1]^[2]^[4]	Artificially delivers the head past a pelvis that the shoulders cannot negotiate; removes the "safety valve" where the head would also not deliver if the shoulders truly cannot fit
Oxytocin augmentation ^[1]	May overcome the natural labour arrest that would otherwise signal disproportion
Previous shoulder dystocia ^[1]^[2]	Reflects persistent maternal anatomy + tendency for similar-sized babies
Post-term pregnancy ^[1]	Continued fetal growth beyond term

50% Are Unpredictable

Approximately 50% of shoulder dystocia cases have NO identifiable risk factors. This is why prediction models perform poorly and why the emphasis must be on universal preparedness rather than selective anticipation. Every birth attendant at every vaginal delivery must know the shoulder dystocia drill ^[1]^[2].

While shoulder dystocia cannot be reliably predicted, certain intrapartum warning signs should make the birth attendant mentally prepare:

Red Flag	Why It Matters
Estimated fetal weight > 4000g (especially > 4500g with diabetes)	Larger bisacromial diameter
Slow progress in second stage despite good contractions	Suggests the shoulders are having difficulty navigating the pelvis
Need for instrumental delivery in a suspected large baby	Forceps/vacuum will deliver the head — but can the shoulders follow?
Previous shoulder dystocia	Recurrence risk ~10–15%
Maternal diabetes with suboptimal glycaemic control	Higher risk of disproportionate macrosomia
Prolonged first stage requiring oxytocin augmentation	Overall picture of potential feto-pelvic disproportion

High Yield Summary — Differential Diagnosis of Shoulder Dystocia

Most common cause of failure to deliver the body after the head: true anterior shoulder dystocia (anterior shoulder behind pubic symphysis)
Key diagnostic feature: Turtle sign + failure of gentle downward traction + need for additional manoeuvres
"Tight shoulders" ≠ shoulder dystocia — no special manoeuvres needed = not shoulder dystocia
Must differentiate from: short/nuchal cord (tethering, not bony impaction), posterior shoulder dystocia (posterior on sacral promontory — suprapubic pressure won't help), bilateral impaction (both shoulders above inlet — worst scenario), fetal anomaly causing body obstruction, locked twins, cervical constriction ring
~50% of cases are unpredictable — universal preparedness > selective prediction
Highest-risk scenario: diabetic macrosomia + instrumental delivery + prolonged second stage
Murtagh's safe diagnostic model: probability diagnosis (true SD), can't miss (bilateral impaction, cord complications), pitfalls (tight shoulders misclassified), masquerade (short cord, fetal anomaly) ^[5]

Active Recall - Differential Diagnosis of Shoulder Dystocia

References

^[1] Lecture slides: Block C - Obstetric Emergency Notes to Students.pdf ^[2] Lecture slides: OBGYN Clinical Test By Topic.pdf ^[3] Lecture slides: GC 224. Hypertension and Pregnancy.pdf (predisposing factors including DM) ^[4] Senior notes: Maksim Surgery Notes.pdf (general principles of instrumental delivery) ^[5] Lecture slides: CFB (FM02) Introduction to common problems - Differentiating the normal from the abnormal.pdf (Murtagh's safe diagnostic model)

Why "Diagnostic Criteria" for Shoulder Dystocia Are Unique

Unlike most medical conditions — where you run blood tests, imaging, and apply formal criteria — shoulder dystocia is a real-time, intrapartum clinical diagnosis made in the moment of delivery. There is no blood test, no imaging, no scoring system. The diagnosis is made when the head has delivered but the shoulders will not follow despite appropriate technique. This makes understanding the diagnostic criteria, the recognition algorithm, and the post-event investigations absolutely essential.

1. Diagnostic Criteria

Shoulder dystocia is diagnosed clinically when ANY of the following are present after delivery of the fetal head: ^[1]^[2]

Criterion	Explanation
1. Need for additional obstetric manoeuvres to deliver the shoulders after gentle downward traction has failed ^[1]^[2]	This is the core criterion. "Additional manoeuvres" = McRoberts positioning, suprapubic pressure, internal rotation, delivery of posterior arm, etc. If the shoulders come with normal or slightly increased routine traction only — it is NOT shoulder dystocia
2. Head-to-body delivery interval > 60 seconds ^[1]^[2]	A surrogate time-based marker. In normal deliveries the body follows the head within seconds. An interval > 60 seconds indicates mechanical obstruction

There Are No Formal 'Diagnostic Criteria' Like KDIGO or DSM-5

Shoulder dystocia does not have a scoring system or laboratory-based diagnostic criteria. It is a clinical event defined by what you observe and what you need to do at the bedside. The "criteria" are descriptive — they define the event retrospectively for documentation, audit, and medicolegal purposes. At the time it happens, you simply recognise it and act.

The diagnosis unfolds in a sequence. These are the clinical features that confirm you are dealing with shoulder dystocia:

Sequence	Clinical Feature	Why It Occurs
Step 1	The "turtle sign" — after head delivery, the head retracts tightly against the perineum ^[1]^[2]	The anterior shoulder is impacted behind the pubic symphysis, pulling the neck (and head) backwards
Step 2	Failure of restitution — the head does not rotate to align with the shoulders	The impacted shoulders prevent the normal 45° rotation
Step 3	Gentle downward traction fails to deliver the anterior shoulder	The anterior shoulder is mechanically blocked by bone (symphysis pubis) — no amount of gentle axial traction will free it
Step 4	Diagnosis confirmed — shoulder dystocia is declared and emergency manoeuvres are initiated	The need for additional manoeuvres beyond routine traction defines the event

Scenario	Why It Is NOT Shoulder Dystocia
"Tight shoulders" — shoulders deliver with slightly increased routine traction, no special manoeuvres needed	Does not meet the definitional criterion of requiring additional obstetric manoeuvres
Delay in delivery due to short/nuchal cord	The obstruction is from cord tethering, not bony impaction
Delay due to cervical constriction ring	The cervix is gripping the neck — the shoulders are not impacted behind bone
Body dystocia from fetal abdominal distension	Obstruction is at the level of the abdomen, not the shoulders

2. Diagnostic Algorithm

2.1 Pre-Delivery: Risk Assessment (Antepartum & Intrapartum)

Shoulder dystocia cannot be reliably predicted, but risk assessment helps the clinician be mentally and practically prepared ^[1]^[2]. This is not a "diagnostic algorithm" in the traditional sense but rather a preparedness algorithm.

Risk Factor	Action
Previous shoulder dystocia ^[1]^[2]	Document details (GA, birth weight, manoeuvres used, injuries); counsel about recurrence risk (~10–15%); consider elective caesarean section if EFW > 4000g or previous severe dystocia
Diabetes (GDM or pre-existing) with suspected macrosomia ^[1]^[3]	Optimise glycaemic control; serial growth scans; consider planned delivery timing; consider elective CS if EFW > 4500g (or > 4000g with diabetes per some guidelines)
Suspected fetal macrosomia (EFW > 4000g) ^[1]^[2]	Note that ultrasound EFW has ±10–15% error; clinical assessment of fetal size; senior obstetrician involvement in delivery plan
Maternal obesity (BMI > 30) ^[1]	Screen for GDM; anticipate larger baby; ensure experienced birth attendant

Warning Sign	What To Do
Prolonged first stage / slow progress requiring augmentation	Consider whether the baby may be too large for the pelvis
Prolonged second stage	Reassess; senior involvement
Need for instrumental delivery in a suspected large baby	Have a senior obstetrician present; prepare for shoulder dystocia; have a clear plan for abandoning instrumental delivery if the head does not deliver easily ^[1]^[2]

After the event, the diagnosis is confirmed by documenting:

The clinical features observed (turtle sign, failed restitution, head-to-body interval)
The manoeuvres performed and their sequence
The personnel present and time of arrival
The head-to-body delivery interval (in minutes and seconds)
Fetal and maternal outcomes (birth weight, Apgar scores, injuries, cord gases)

Documentation Is Crucial

Shoulder dystocia is one of the most medicolegally contested obstetric events. Contemporaneous, detailed documentation of the timeline, the manoeuvres used (in order), and the outcomes is essential. Many units use a structured proforma. If you were there, write your own note as well ^[1]^[2].

3. Investigations

Unlike most conditions where investigations confirm the diagnosis, in shoulder dystocia:

No investigation is needed to MAKE the diagnosis — it is made clinically at the bedside in real-time
Antepartum investigations help identify risk factors and aid preparedness (but cannot reliably predict shoulder dystocia)
Post-event investigations assess for complications (to both mother and baby)

Investigation	Key Findings & Interpretation	Why It Matters
Ultrasound estimation of fetal weight (EFW) ^[1]^[2]	EFW > 4000g suggests macrosomia; EFW > 4500g is the usual threshold for considering elective CS in diabetic pregnancies	Limitation: accuracy is ±10–15% (i.e., a baby estimated at 4000g could actually weigh 3400–4600g). Poor positive predictive value for shoulder dystocia. Cannot measure the bisacromial diameter reliably
Abdominal circumference (AC) on ultrasound ^[1]	AC > 95th centile or AC growing disproportionately faster than head circumference (HC) suggests disproportionate macrosomia (trunk > head) — the pattern seen in diabetic macrosomia	A rising AC-to-HC ratio is more concerning than an absolutely large baby with proportionate growth
Oral glucose tolerance test (OGTT) for GDM ^[3]^[6]	Diagnosis of GDM if fasting glucose ≥ 5.1 mmol/L, 1-hour ≥ 10.0 mmol/L, or 2-hour ≥ 8.5 mmol/L (IADPSG criteria) ^[3]^[6]	Identifies diabetic mothers at risk of disproportionate macrosomia. Good glycaemic control reduces but does not eliminate macrosomia risk
HbA1c / glycaemic monitoring	HbA1c reflects average glucose control over 2–3 months; capillary glucose monitoring guides insulin adjustments	Poor glycaemic control → higher risk of macrosomia → higher risk of shoulder dystocia
Clinical estimation of fetal size	Symphysis-fundal height (SFH) measurement; clinical palpation of fetal size	SFH > dates may suggest macrosomia. Clinical estimation is no more accurate than ultrasound for predicting macrosomia
Pelvimetry (clinical or radiological)	Assessment of maternal pelvic dimensions	NOT recommended routinely — pelvimetry does not reliably predict shoulder dystocia and is essentially abandoned in modern practice

Ultrasound Cannot Predict Shoulder Dystocia

The positive predictive value of ultrasound EFW for shoulder dystocia is extremely poor (< 30%). If you offered elective CS to every woman with an EFW > 4000g, you would perform hundreds of unnecessary caesarean sections to prevent one case of shoulder dystocia. This is why routine induction or CS based on suspected macrosomia alone is NOT recommended unless there are additional risk factors (e.g., diabetes + EFW > 4500g) ^[1]^[2].

Investigation	Role
Continuous electronic fetal monitoring (CTG)	Not diagnostic of shoulder dystocia but may show fetal distress patterns (e.g., variable decelerations from cord compression) that heighten vigilance. A normal CTG does NOT exclude subsequent shoulder dystocia
Partogram (labour progress chart)	Prolonged first or second stage, slow cervical dilatation, or need for oxytocin augmentation may signal potential feto-pelvic disproportion
Clinical assessment during second stage	Senior obstetrician assessment of descent, station, and position before instrumental delivery

3.4 Post-Event Investigations (After Delivery)

These investigations are performed to assess for complications in both the neonate and the mother:

Investigation	Key Findings	Interpretation
Paired umbilical cord blood gas (arterial and venous) ^[1]^[2]	Arterial pH, base excess, lactate	Most important post-delivery investigation. Arterial pH < 7.0 and/or base excess < -12 mmol/L indicates significant metabolic acidosis (hypoxia during the event). The pH drops ~0.04 units per minute during shoulder dystocia → cord gases help quantify the duration and severity of hypoxia
Apgar score at 1 and 5 minutes ^[1]^[2]	Scores of 0–3 at 5 min indicate severe compromise	Apgar reflects the baby's overall condition. Low Apgar may indicate need for resuscitation and further workup
Neonatal neurological examination	Assess for brachial plexus injury (Erb palsy: waiter's tip; Klumpke: claw hand; total: flail arm); assess for asymmetric Moro reflex	Documents nerve injury; most (80–90%) Erb palsies resolve within 6–12 months, but early documentation is crucial for tracking recovery and medicolegal purposes
Skeletal assessment	Palpate clavicles and humeri for crepitus, swelling, or asymmetry	Clavicular fracture (most common fracture in shoulder dystocia) and humeral fracture should be actively sought. May be asymptomatic initially
X-ray of clavicle / humerus	Fracture line, displacement	If clinical suspicion of fracture (crepitus, pseudoparalysis, swelling). Note: some clavicular fractures are deliberately caused as a manoeuvre to reduce the bisacromial diameter
Blood glucose monitoring (neonatal)	Hypoglycaemia (< 2.6 mmol/L)	Macrosomic / diabetic-mother babies are at high risk of neonatal hypoglycaemia due to fetal hyperinsulinism persisting after delivery (the placental glucose supply is suddenly cut off but the baby's insulin remains high)
FBC, electrolytes	Anaemia (if blood loss), electrolyte disturbance	Baseline assessment, especially if the baby required resuscitation
MRI of brachial plexus	Nerve root avulsion vs stretch injury (neuropraxia)	Only if brachial plexus palsy does NOT recover within 3–6 months; helps plan surgical intervention (nerve grafting/transfer)

Investigation	Key Findings	Interpretation
Assessment for perineal tears	1st–4th degree tears; cervical lacerations	Manoeuvres during shoulder dystocia can cause or extend tears. Always perform a systematic genital tract inspection after delivery
Estimated blood loss + haemoglobin	Excessive blood loss (PPH > 500 mL vaginal, > 1000 mL CS)	Shoulder dystocia increases risk of PPH from uterine atony (prolonged/traumatic delivery) and genital tract lacerations
Coagulation screen (if significant PPH)	PT, aPTT, fibrinogen	DIC can occur in massive PPH; fibrinogen < 2 g/L is an early predictor of severe PPH
Group and save / crossmatch	Blood group, antibody screen	Anticipate need for transfusion if PPH occurs
Bladder assessment	Urinary retention, haematuria	Bladder injury or urethral trauma from manoeuvres; catheterise and monitor urine output
Psychological assessment	Screen for acute stress reaction, risk of PTSD/postnatal depression	Traumatic birth experience — both the mother and the clinician can be affected

Timing	Investigation	Purpose
Antepartum	USS for EFW, AC, HC	Risk stratification (not diagnostic)
Antepartum	OGTT / HbA1c	Diagnose GDM → identify at-risk pregnancies
Antepartum	SFH measurement	Clinical screening for macrosomia
Intrapartum	CTG	Monitor fetal wellbeing (not predictive of SD)
Intrapartum	Partogram	Identify prolonged labour suggesting disproportion
Intrapartum	Clinical recognition	DIAGNOSTIC — turtle sign, failed traction
Post-event (Neonate)	Paired cord blood gas	Quantify hypoxia severity
Post-event (Neonate)	Neurological exam	Detect brachial plexus injury
Post-event (Neonate)	Skeletal assessment ± XR	Detect clavicular/humeral fracture
Post-event (Neonate)	Blood glucose monitoring	Detect neonatal hypoglycaemia
Post-event (Mother)	Genital tract inspection	Detect perineal tears, cervical lacerations
Post-event (Mother)	CBC, coagulation, G&S	Assess for PPH, prepare for transfusion
Post-event (Mother)	Psychological assessment	Screen for acute stress / PTSD risk

Because cord blood gas is the single most important post-event investigation, let's break it down:

Parameter	Normal Range	In Shoulder Dystocia	Interpretation
Arterial pH	7.18–7.38	Often < 7.10	pH < 7.0 = significant acidosis; correlates with risk of HIE
Arterial base excess	-2 to -8 mmol/L	Often < -12	Reflects duration of metabolic (anaerobic) acidosis
Arterial pCO₂	40–60 mmHg	May be elevated	Respiratory component from impaired ventilation (chest compressed)
Arterial pO₂	15–25 mmHg	Decreased	Reflects reduced oxygenation during impaction
Lactate	< 5 mmol/L	Elevated	Anaerobic metabolism during hypoxia

Why paired (arterial AND venous)?

The arterial sample reflects the fetal metabolic state (what is coming FROM the baby)
The venous sample reflects what the placenta is delivering TO the baby
A large arterial-venous difference suggests an acute event (the baby was actively consuming oxygen and producing acid faster than the placenta could compensate) — consistent with acute cord compression in shoulder dystocia
If both are equally acidotic, this suggests a more prolonged process

Cord Gas Collection Is TIME-SENSITIVE

Cord blood gas must be collected within 60 minutes of delivery (ideally immediately by double-clamping a segment of cord). Delayed sampling allows ongoing metabolic changes in the clamped segment and makes the results unreliable. After a shoulder dystocia event, ensuring cord gases are taken should be a reflex action ^[1]^[2].

High Yield Summary — Diagnostic Criteria, Algorithm & Investigations

Diagnosis is CLINICAL and made in REAL-TIME: turtle sign + failure of gentle downward traction + need for additional obstetric manoeuvres (or head-to-body interval > 60 seconds)
No blood test, imaging, or scoring system diagnoses shoulder dystocia — it is an intrapartum event
Antepartum investigations (USS for EFW, OGTT for GDM) are for RISK STRATIFICATION only — they cannot predict shoulder dystocia reliably (PPV < 30%)
USS EFW has ±10-15% error — this is why routine CS for suspected macrosomia alone is not recommended
~50% of cases occur without identifiable risk factors → universal preparedness over selective prediction
Post-event investigations focus on complications:
- Neonate: Paired cord blood gas (most important), Apgar, neurological exam (brachial plexus), skeletal assessment (clavicle/humerus fracture), blood glucose
- Mother: Genital tract inspection (tears), blood loss assessment, coagulation screen if PPH, psychological screening
Paired cord blood gas must be taken within 60 minutes; arterial pH < 7.0 and/or base excess < -12 indicates significant acidosis
Documentation is crucial — record timeline, manoeuvres (in sequence), personnel, outcomes; use structured proforma

Active Recall - Diagnostic Criteria, Algorithm & Investigations for Shoulder Dystocia

^[1] Lecture slides: Block C - Obstetric Emergency Notes to Students.pdf ^[2] Lecture slides: OBGYN Clinical Test By Topic.pdf ^[3] Lecture slides: GC 224. Hypertension and Pregnancy.pdf (predisposing factors including DM) ^[5] Lecture slides: CFB (FM02) Introduction to common problems - Differentiating the normal from the abnormal.pdf (Murtagh's safe diagnostic model) ^[6] Senior notes: Ryan Ho Chemical Path.pdf (OGTT diagnostic criteria)

Overarching Principle

Shoulder dystocia is a time-critical obstetric emergency. Every second matters — the umbilical cord is compressed, the thorax cannot expand, and fetal pH drops approximately 0.04 units per minute. Irreversible brain injury can occur within 4–8 minutes ^[1]^[2]. The management is entirely mechanical — there are no drugs that "treat" shoulder dystocia itself (though tocolytics can assist specific manoeuvres). The key to successful management is a well-rehearsed, systematic drill performed by a coordinated team.

The Single Most Important Factor in Shoulder Dystocia Outcomes

The outcome depends on how quickly and calmly the team executes a structured drill. This is why simulation training is mandatory in all obstetric units. Studies consistently show that units with regular shoulder dystocia drills have lower complication rates ^[1]^[2].

1. Preparation and Prevention

While shoulder dystocia cannot be reliably predicted or prevented, certain situations warrant advance planning:

Scenario	Management Strategy	Rationale
Previous shoulder dystocia ^[1]^[2]	Document previous details (GA, birth weight, manoeuvres, injuries). Counsel about recurrence (~10–15%). Consider elective caesarean section if previous severe shoulder dystocia or EFW > 4000g in current pregnancy	Persistent maternal pelvic anatomy + tendency for similar-sized babies
Diabetes + EFW > 4500g ^[1]^[2]	Offer elective caesarean section	Disproportionate macrosomia significantly increases risk
Non-diabetic + EFW > 5000g ^[1]	Offer elective caesarean section	Absolute fetal size makes shoulder dystocia very likely
Diabetes + EFW 4000–4500g	Individualised discussion; consider CS; if vaginal delivery planned, ensure senior obstetrician present	Borderline zone — shared decision-making
Suspected macrosomia without diabetes	Vaginal delivery generally appropriate; ensure preparedness	Induction for suspected macrosomia alone has NOT been shown to reduce shoulder dystocia

Induction for Suspected Macrosomia

Routine induction of labour for suspected macrosomia in non-diabetic women is controversial and generally not recommended. The ARRIVE trial and other studies show that while induction may modestly reduce birth weight, it does not significantly reduce shoulder dystocia rates, and ultrasound estimation has a ±10–15% error margin. However, in diabetic women with EFW > 4000g, planned delivery (induction or CS) is more strongly considered ^[1]^[2].

Shoulder dystocia is an intrapartum risk factor for anticipation of neonatal resuscitation need ^[7].

Action	Detail
Ensure neonatal resuscitation team is available ^[7]	Shoulder dystocia is listed among intrapartum risk factors requiring anticipation of resuscitation need
Experienced birth attendant	Senior midwife and/or obstetrician for high-risk deliveries
Equipment check	Ensure neonatal resuscitation equipment is ready
Team briefing	If risk factors are identified, brief the team and assign roles before delivery
Avoid excessive fundal pressure	NEVER apply fundal pressure during suspected shoulder dystocia — it pushes the anterior shoulder further into the symphysis and increases impaction ^[1]^[2]

The internationally recognised structured approach to managing shoulder dystocia is the HELPERR mnemonic (from the ALSO — Advanced Life Support in Obstetrics — programme). This provides a stepwise escalation from simple external manoeuvres to complex internal manoeuvres to last-resort procedures ^[1]^[2].

HELPERR stands for:

H = Call for Help
E = Evaluate for Episiotomy
L = Legs (McRoberts manoeuvre)
P = Pressure (Suprapubic)
E = Enter (Internal manoeuvres — Rubin II, Wood's screw)
R = Remove the posterior arm
R = Roll the patient (Gaskin manoeuvre — all-fours position)

High Yield Exam Mnemonic — HELPERR

HELPERR is the standard mnemonic for shoulder dystocia management and is extremely high-yield for exams. You must know each step, the sequence, the mechanism, and why it works. ^[1]^[2]

Step-by-Step HELPERR Algorithm

3. Detailed Explanation of Each HELPERR Step

Action	Detail
Who to call	Senior obstetrician, additional midwife, anaesthetist, neonatal team (paediatrician + neonatal nurse)
Note the time	Start the clock — document the exact time shoulder dystocia is recognised
Do NOT apply excessive traction to the fetal head ^[1]^[2]	Excessive lateral traction stretches the brachial plexus (C5–T1) between the fixed cervical spine and the impacted shoulder → Erb palsy. The instinct to "pull harder" must be actively resisted
Do NOT apply fundal pressure ^[1]^[2]	Fundal pressure pushes the fetal trunk downward, impacting the anterior shoulder even more firmly behind the symphysis. It worsens impaction and increases the risk of uterine rupture

Two Things You Must NEVER Do

1. NEVER apply excessive lateral traction to the head — this causes brachial plexus injury. 2. NEVER apply fundal pressure — this worsens impaction. These are the two most dangerous errors in shoulder dystocia management. Both are examined frequently ^[1]^[2].

Aspect	Detail
Purpose	Episiotomy does NOT relieve the bony obstruction (the shoulder is stuck behind bone, not soft tissue). However, it creates more room for the clinician's hand to perform internal manoeuvres (Rubin II, Wood's screw, posterior arm delivery) ^[1]^[2]
When	Consider at any point if internal manoeuvres are anticipated; ideally early to facilitate access
Type	Mediolateral episiotomy (standard in the UK/HK)
Contraindication	None in this emergency — the benefit of enabling internal manoeuvres outweighs any risk

Why doesn't episiotomy relieve the obstruction? Because the problem is the anterior shoulder impacted behind the pubic symphysis — which is a bony structure. Cutting the perineum (soft tissue posteriorly) does not change the relationship between the shoulder and the bone anteriorly. But it creates space posteriorly for the clinician's hand.

McRoberts manoeuvre is the single most effective first-line manoeuvre for shoulder dystocia. ^[1]^[2]

Aspect	Detail
Technique	Sharply flex the mother's thighs onto her abdomen (hyperflexion of the hips), with the knees drawn up towards the shoulders. Each leg is held by an assistant. Remove the legs from stirrups/lithotomy poles if applicable
Mechanism	Hyperflexion of the hips: (1) Straightens the sacrum relative to the lumbar spine, removing the sacral promontory as an obstruction to the posterior shoulder; (2) Rotates the pubic symphysis cephalad (upward), which effectively increases the AP diameter of the pelvic inlet by ~1–2 cm; (3) Pushes the posterior shoulder over the sacral promontory into the pelvis. Together, these changes "open up" the pelvic inlet
Success rate	Resolves ~40–50% of shoulder dystocia cases when combined with suprapubic pressure ^[1]^[2]
Contraindication	Avoid with dense regional anaesthesia if there is a risk of hip dislocation (extremely rare); otherwise, there are essentially no contraindications

Why is McRoberts so effective? Think of the pelvis as a rigid ring that can be "tilted." Hyperflexing the hips tilts the pelvic inlet anteriorly, changing the angle at which the fetal shoulders meet the pubic symphysis. The symphysis effectively lifts away from the anterior shoulder, and the posterior shoulder drops past the sacral promontory. No internal manipulation is needed, making it the safest and fastest first manoeuvre.

Applied simultaneously with McRoberts for maximum effect. ^[1]^[2]

Aspect	Detail
Technique	Apply firm, directed pressure from the MOTHER'S SIDE (not the front) over the posterior aspect of the anterior shoulder. This pushes the anterior shoulder anteriorly (away from the symphysis) and into an oblique diameter. Can be applied as continuous pressure or a rocking motion
Direction	The pressure should push the anterior shoulder towards the baby's chest (adduction), NOT towards its back. Think of it as trying to "push the shoulder off the shelf" of the symphysis and rotate it into the oblique
Mechanism	(1) Dislodges the anterior shoulder from behind the symphysis; (2) Reduces the bisacromial diameter by adducting the shoulders; (3) Rotates the bisacromial diameter from the (shorter) AP into the (longer) oblique diameter
NOT to be confused with fundal pressure ^[1]^[2]	Suprapubic pressure is applied over the suprapubic area (just above the pubic bone, pressing on the posterior aspect of the anterior shoulder). Fundal pressure is applied on top of the uterus — this is CONTRAINDICATED

How to locate where to press: The clinician performing the delivery should feel where the anterior shoulder is and direct the assistant to press in the correct location — just above the symphysis pubis, on the side where the fetal back is.

Feature	Suprapubic Pressure ✓	Fundal Pressure ✗
Site of application	Just above pubic symphysis	Top of uterine fundus
Direction of force	Laterally and downward on anterior shoulder	Downward on fetal trunk
Effect on impaction	Relieves — pushes shoulder off symphysis	Worsens — pushes shoulder deeper into symphysis
Indication	ALWAYS in shoulder dystocia	NEVER in shoulder dystocia

E — Enter: Internal Manoeuvres (Rubin II and Wood's Screw)

If McRoberts + suprapubic pressure fail (i.e., the ~50% of cases not resolved by first-line manoeuvres), escalate to internal manoeuvres ^[1]^[2].

An episiotomy should be performed (if not already done) to create space for the clinician's hand.

Aspect	Detail
Technique	Insert a hand vaginally behind the anterior shoulder and push it towards the fetal chest (adduction), rotating it into the oblique diameter
Mechanism	Adducts the anterior shoulder → reduces the bisacromial diameter. Also rotates the shoulder off the symphysis
Named after	Allan Rubin (Rubin I = suprapubic pressure; Rubin II = internal rotation)

Aspect	Detail
Technique	Insert a hand behind the posterior shoulder and push it towards the fetal back (abduction), rotating the baby 180° like a screw. This moves the anterior shoulder off the symphysis
Mechanism	Rotates the entire fetus within the pelvis so that the previously posterior shoulder becomes the new anterior shoulder and can slip under the symphysis. Named because the motion is like turning a screw (the corkscrew principle)
Reverse Wood's screw	If Wood's screw fails, try the opposite direction of rotation

Aspect	Detail
Technique	One hand on the anterior shoulder (Rubin II — push towards chest) and one hand on the posterior shoulder (Wood's — push towards back). Both hands work together to rotate the fetus
Mechanism	The two hands apply rotational force in the same direction, like a wrench turning a bolt. This is the most effective internal rotation technique

Delivery of the posterior arm is one of the most reliable manoeuvres and has the highest individual success rate (~85%) of any single manoeuvre. ^[1]^[2]

Aspect	Detail
Technique	(1) The clinician inserts a hand along the fetal chest to reach the posterior arm. (2) Identify the posterior elbow and flex it. (3) Sweep the forearm across the fetal chest and face. (4) Grasp the hand/wrist and deliver the arm out of the vagina
Mechanism	Delivering the posterior arm reduces the bisacromial diameter by approximately 20% (the diameter is effectively reduced from the shoulder-to-shoulder width to the shoulder-to-elbow width). This creates enough room for the anterior shoulder to slip under the symphysis
Risk	Humeral fracture (the most common complication of this manoeuvre, occurring in ~2–5% of attempts); however, neonatal humeral fractures heal rapidly and completely without long-term sequelae
When to use	Can be attempted at any point; some experts advocate trying it earlier than HELPERR suggests, given its high success rate

Why is it so effective? Consider the geometry: the bisacromial diameter (shoulder-to-shoulder) is typically ~12 cm. If you deliver one arm, the effective diameter becomes the shoulder-to-axilla distance, which is approximately 9.5 cm — easily fitting through the ~11 cm AP diameter of the pelvic inlet. It is the most mechanically logical manoeuvre.

Aspect	Detail
Technique	Roll the mother onto all fours (hands and knees position)
Mechanism	(1) Gravity assists — the fetal weight falls away from the pubic symphysis. (2) The pelvic diameters change with position — the AP diameter of the inlet increases slightly in all-fours. (3) The sacrum is free to move posteriorly (no longer compressed against the bed), increasing the effective pelvic outlet size. (4) Sometimes the posterior shoulder delivers first in this position
Success rate	Reports suggest ~83% success rate, but often used after other manoeuvres have failed, so the residual cases may be easier
Practical limitation	Difficult if the mother has dense epidural anaesthesia (cannot support herself on hands and knees); requires at least two assistants to reposition the mother safely
Contraindication	Dense neuraxial blockade preventing weight-bearing; mother physically unable to assume position

4. Last-Resort Manoeuvres

If ALL of the above HELPERR steps fail, the following last-resort manoeuvres are considered. These carry significant morbidity but are life-saving ^[1]^[2]:

Aspect	Detail
What it is	Reversal of the mechanism of delivery: the fetal head is flexed and pushed back into the vagina/uterus, followed by emergency caesarean section
Named after	William A. Zavanelli
Technique	(1) Flex the fetal head (reverse restitution). (2) Apply constant, firm pressure to push the head back into the vagina. (3) Hold the head in place. (4) Perform emergency category 1 caesarean section immediately
Mechanism	If the shoulders cannot be delivered vaginally, the only option is abdominal delivery. To do this, the head must be returned to the uterus
When to use	Only when ALL other manoeuvres have failed; the baby is likely severely compromised by this point
Tocolysis	Administer a tocolytic (sublingual GTN 400mcg spray or IV terbutaline 0.25mg) to relax the uterus — this facilitates replacement of the head and may also help relax the lower uterine segment around the shoulders
Success rate	~90% when attempted, but outcomes depend on the duration of impaction
Complications	Uterine rupture, cervical lacerations, fetal injury, maternal psychological trauma

Aspect	Detail
What it is	Deliberate surgical division of the pubic symphysis cartilage to widen the pelvic inlet
Technique	A scalpel is used to cut the fibrous cartilage of the symphysis pubis under local anaesthesia, while an assistant supports the urethra laterally with a catheter to protect it
Mechanism	Cutting the symphysis allows the two halves of the pelvis to separate by 1–2.5 cm, widening the AP and transverse diameters of the inlet sufficiently to allow the impacted shoulder to pass
When to use	Absolute last resort; more commonly described in resource-limited settings where emergency CS is not immediately available
Complications	Haemorrhage, bladder/urethral injury, long-term pelvic instability, osteitis pubis, chronic pain
In Hong Kong	Extremely rarely performed; emergency CS via Zavanelli is generally preferred as operative theatres are available

Aspect	Detail
What it is	Intentional fracture of the anterior fetal clavicle to reduce the bisacromial diameter
Technique	Apply direct pressure over the mid-clavicle, pushing it towards the chest. This is technically difficult because the clavicle is surrounded by soft tissue and is hard to isolate
Mechanism	Fracturing the clavicle allows the shoulder to collapse inward, effectively reducing the bisacromial diameter by ~1.5–2 cm
When to use	Last resort; often attempted but rarely successful because the clavicle is difficult to fracture deliberately
Complications	Pneumothorax (rare), subclavian vessel injury (rare). Clavicular fractures in neonates heal rapidly without long-term sequelae

Aspect	Detail
What it is	Emergency hysterotomy (uterine incision) to push the anterior shoulder from above while an assistant applies traction from below
Technique	Perform an emergency laparotomy and hysterotomy; an assistant's hand is inserted through the uterine incision to push the impacted shoulder downward/rotate it, while the delivery is completed vaginally
When to use	When Zavanelli + CS is not feasible (e.g., head cannot be replaced)
Complications	Major maternal surgical morbidity

Manoeuvre	Mechanism	Success Rate	Key Risk
McRoberts ^[1]^[2]	Straightens sacrum, rotates symphysis cephalad, increases AP inlet	~40–50% (with suprapubic pressure)	Minimal — safest manoeuvre
Suprapubic pressure ^[1]^[2]	Dislodges anterior shoulder, adducts and rotates into oblique	Used with McRoberts	Minimal
Rubin II	Internal rotation of anterior shoulder (adduction)	Variable; often combined with Wood's	Vaginal/cervical lacerations
Wood's screw	Rotates fetus 180° to free impacted shoulder	Variable	Vaginal/cervical lacerations
Posterior arm delivery ^[1]^[2]	Reduces bisacromial diameter by ~20%	~85% individually	Humeral fracture (~2–5%)
Gaskin (all-fours)	Gravity + increased pelvic diameters	~83%	Difficult with epidural
Zavanelli	Head replaced → emergency CS	~90%	Uterine rupture, fetal/maternal injury
Symphysiotomy	Widens pelvis by dividing symphysis	High	Bladder injury, pelvic instability
Deliberate clavicular fracture	Reduces bisacromial diameter	Low (technically difficult)	Pneumothorax (rare)

6. Post-Delivery Management

Action	Rationale
Anticipate need for neonatal resuscitation ^[7]	Shoulder dystocia is a recognised intrapartum risk factor for neonatal compromise
Immediate assessment (Apgar, tone, colour, HR, respiration)	The baby may be hypoxic, acidotic, and require resuscitation
Neonatal resuscitation as per NRP algorithm if needed	Stimulate → airway → breathing → circulation → drugs
Paired cord blood gas (arterial + venous)	Quantify hypoxia severity (pH, BE, lactate)
Examine for brachial plexus injury	Check Moro reflex symmetry; check for waiter's tip (Erb) or claw hand (Klumpke)
Examine for fractures	Palpate clavicles and humeri bilaterally
Blood glucose monitoring	Neonatal hypoglycaemia risk (especially in diabetic-mother/macrosomic babies)
Admit to NICU/SCBU if compromise present	For monitoring, observation, treatment

Action	Rationale
Systematic genital tract inspection	Identify perineal tears (3rd/4th degree), cervical lacerations, vaginal lacerations from manoeuvres
Repair episiotomy and any tears	Primary repair under anaesthesia; 3rd/4th degree tears require repair in theatre by experienced surgeon
Monitor for postpartum haemorrhage	Uterine atony (from prolonged/traumatic delivery) and genital tract lacerations both contribute
Active management of third stage	Oxytocin, controlled cord traction, uterine massage
Catheterisation and monitor urine output	Assess for bladder injury or urethral trauma
Debrief with the mother and partner	Explain what happened, why, what was done, the baby's condition, and future pregnancy implications
Psychological support	Screen for acute stress reaction; arrange follow-up for PTSD/postnatal depression
Thromboprophylaxis assessment	Traumatic delivery is a risk factor for VTE

Element	Detail
Structured proforma ^[1]^[2]	Many units use a dedicated shoulder dystocia documentation form
Time of head delivery	Start of the event
Time of body delivery	End of the event (calculate head-to-body interval)
Manoeuvres performed (in order)	Document each manoeuvre attempted, whether it was successful, and in what sequence
Personnel present	Names, roles, time of arrival
Fetal condition at birth	Apgar scores, cord gases, injuries identified
Maternal condition	Tears, blood loss, injuries
Debrief note	That the mother/partner was counselled

Topic	Advice
Recurrence risk ^[1]^[2]	~10–15% in subsequent pregnancies
Mode of delivery in next pregnancy	Consider elective CS if: previous severe shoulder dystocia, previous neonatal injury, large EFW in current pregnancy
GDM screening	If GDM was present, rescreen with OGTT at 6–12 weeks postpartum and in subsequent pregnancies
Neonatal follow-up	If brachial plexus injury: physiotherapy, review at 3–6 months, MRI and surgical referral if no recovery by 6 months

8. Contraindications and Special Considerations

Action	Why It Is Contraindicated
Excessive lateral traction on fetal head ^[1]^[2]	Stretches brachial plexus → Erb/Klumpke palsy. The head should be held, not pulled
Fundal pressure ^[1]^[2]	Pushes anterior shoulder deeper behind symphysis; worsens impaction; risk of uterine rupture
Pivoting/levering the head ("Pajot manoeuvre")	Excessive force on the cervical spine → risk of cervical spine injury

Manoeuvre	Relative Contraindication	Workaround
Gaskin (all-fours)	Dense epidural/spinal anaesthesia (mother cannot support weight)	Use McRoberts and internal manoeuvres instead; or attempt lateral position
Zavanelli	Advanced fetal decomposition; very prolonged impaction with likely fetal demise	Symphysiotomy or destructive delivery if fetus non-viable
Symphysiotomy	Facilities for emergency CS available (preferred alternative: Zavanelli + CS)	In well-resourced settings, Zavanelli is preferred

Agent	Dose	Purpose
Sublingual GTN spray	400 mcg	Relaxes uterus → facilitates Zavanelli manoeuvre (head replacement); may also relax the lower uterine segment to allow more room for internal manoeuvres
IV Terbutaline	0.25 mg SC or IV	Alternative tocolytic for uterine relaxation

Why tocolysis? The uterus continues to contract during shoulder dystocia, which (1) pushes the fetus against the impacted shoulder (worsening impaction), and (2) makes it harder to push the head back in for Zavanelli. Relaxing the uterus creates a "window" to perform the manoeuvre.

High Yield Summary — Management of Shoulder Dystocia

HELPERR mnemonic is the standard management algorithm — must know each step, the mechanism, and the sequence ^[1]^[2]
McRoberts + suprapubic pressure resolves ~40–50% of cases — always start here (first-line, safest, fastest)
Posterior arm delivery has the highest individual success rate (~85%) — reduces bisacromial diameter by ~20%
NEVER apply excessive lateral traction (causes brachial plexus injury) or fundal pressure (worsens impaction) ^[1]^[2]
Episiotomy does NOT relieve bony obstruction but creates space for internal manoeuvres
Gaskin manoeuvre (all-fours) uses gravity and changes pelvic diameters but is limited by epidural anaesthesia
Last-resort manoeuvres: Zavanelli (cephalic replacement → emergency CS), symphysiotomy, deliberate clavicular fracture
Post-event: cord gases, neonatal exam (brachial plexus, fractures, glucose), maternal assessment (tears, PPH, psychology), structured documentation, future pregnancy counselling
Shoulder dystocia is a recognised intrapartum risk factor for anticipation of neonatal resuscitation ^[7]
~50% of cases are unpredictable → ALL birth attendants must be trained through simulation drills

Active Recall - Management of Shoulder Dystocia

^[1] Lecture slides: Block C - Obstetric Emergency Notes to Students.pdf ^[2] Lecture slides: OBGYN Clinical Test By Topic.pdf ^[7] Lecture slides: CFB (OGPAE01-2) Perinatal Medicine, Antenatal Care and Pre-pregnant Counselling (Part II).pdf

Overview

Shoulder dystocia complications affect both the neonate and the mother. Understanding these complications requires connecting them back to the underlying mechanical problem — an anterior shoulder impacted behind the pubic symphysis, with the fetal thorax compressed in the birth canal and the umbilical cord under compression. Every complication flows logically from either (1) the hypoxic insult during impaction, (2) the mechanical forces during delivery manoeuvres, or (3) the traumatic nature of the event itself.

1. Fetal / Neonatal Complications

1.1 Brachial Plexus Injury (BPI)

Brachial plexus injury is the signature complication of shoulder dystocia and the most commonly examined. ^[1]^[2]

Incidence: Occurs in approximately 2.3–16% of shoulder dystocia deliveries ^[1]^[2]. Of these, approximately 80–90% resolve spontaneously within 6–12 months (neuropraxia). Permanent injury occurs in approximately 10–20%.

The brachial plexus is a network of nerves formed from the ventral rami of C5–T1. It runs from the neck, through the scalene triangle, over the first rib, and into the axilla to supply motor and sensory innervation to the upper limb.

Why does BPI occur in shoulder dystocia?

During shoulder dystocia, when traction (even gentle traction) is applied to the fetal head to try to free the impacted anterior shoulder:

The head is pulled laterally away from the anterior shoulder
The anterior shoulder is fixed behind the pubic symphysis
The brachial plexus on the side of the anterior shoulder is stretched between two fixed points: the cervical spine (which moves with the head) and the shoulder (which is anchored by the symphysis)
This lateral stretch injures the nerve roots, most commonly the upper roots (C5–C6) because they are the first to be put under tension

BPI Can Occur WITHOUT Excessive Traction

Brachial plexus injury can also result from endogenous forces — maternal pushing and uterine contractions — without ANY clinician-applied traction. This is an important medicolegal point. Studies have documented BPI in caesarean sections (where no traction is applied to the head at all), proving that endogenous forces alone can cause the injury. Posterior shoulder BPI (affecting the arm that was NOT impacted) also occurs, further supporting the role of endogenous forces ^[1]^[2].

Type	Nerve Roots	Clinical Presentation	Mechanism	Prognosis
Erb-Duchenne palsy (most common, ~80%)	C5–C6 (± C7)	"Waiter's tip" posture: arm adducted, internally rotated, elbow extended, forearm pronated, wrist flexed. Loss of shoulder abduction, external rotation, elbow flexion, forearm supination	Upper trunk stretched by lateral head traction while shoulder is impacted. C5 supplies deltoid (abduction), supraspinatus (initiation of abduction), biceps (elbow flexion); C6 supplies biceps, brachioradialis, wrist extensors	Good — 80–90% recover spontaneously within 6–12 months (neuropraxia)
Klumpke palsy (rare in isolation)	C8–T1	"Claw hand": hyperextension at MCP joints, flexion at IP joints. Loss of intrinsic hand muscles (interossei, lumbricals). ± Horner syndrome (T1 sympathetic fibres disrupted → miosis, ptosis, anhidrosis)	Lower trunk stretched, typically from excessive upward traction on the arm or during posterior arm delivery	Poorer — lower roots are more vulnerable to avulsion (nerve torn from spinal cord)
Total plexus palsy	C5–T1	Flail arm: complete paralysis of the upper limb. No movement at shoulder, elbow, wrist, or hand	Severe stretch or avulsion of entire plexus	Worst prognosis; often requires surgical intervention

Grade	Type	Pathology	Recovery
Neuropraxia	Stretch without structural damage	Temporary conduction block; myelin sheath disrupted but axon intact	Full recovery within weeks to months
Axonotmesis	Axon disrupted but nerve sheath intact	Wallerian degeneration distal to injury; axon regrows along intact sheath	Partial recovery over months; may be incomplete
Neurotmesis	Complete nerve disruption or avulsion	Axon AND sheath disrupted; no pathway for regrowth. Avulsion = root torn from spinal cord	No spontaneous recovery; requires surgical repair (nerve grafting, nerve transfer)

Timing	Action
Immediate	Document examination findings; photograph the posture; immobilise gently in position of comfort
First 2–3 weeks	Gentle passive range-of-motion exercises by physiotherapist to prevent joint contractures
3–6 months	Regular reassessment; most neuropraxia recovers by this time. Serial clinical examination documenting recovery of biceps function (elbow flexion against gravity)
6–9 months (if no recovery)	MRI of brachial plexus (to differentiate stretch from avulsion); EMG/NCS; referral to specialist for surgical exploration
Surgery	Nerve grafting (using sural nerve), nerve transfer (e.g., Oberlin transfer — ulnar nerve fascicle to biceps motor branch), tendon transfers for late presentations

1.2 Fractures

Incidence: Most common fracture in shoulder dystocia (~2–10% of cases) ^[1]^[2]

Aspect	Detail
Mechanism	The clavicle is compressed between the impacted anterior shoulder and the pubic symphysis. May also occur during deliberate attempts to fracture the clavicle (as a last-resort manoeuvre to reduce bisacromial diameter)
Clinical features	Crepitus over clavicle; pseudoparalysis (baby does not move the arm — mimics brachial plexus injury); swelling; asymmetric Moro reflex. May be asymptomatic initially and found incidentally on examination or X-ray
Differentiation from BPI	In clavicular fracture: the hand and fingers move normally (grasp reflex intact), but the baby avoids moving the whole arm due to pain. In Erb palsy: specific muscle groups are paralysed (deltoid, biceps, etc.) and the waiter's tip posture is present
Investigation	AP chest X-ray — shows fracture line, usually in middle third. Note that greenstick fractures may be subtle
Prognosis	Excellent — neonatal clavicular fractures heal rapidly within 2–3 weeks with callus formation. No specific treatment beyond gentle handling is required. Parents should be reassured

Incidence: Less common than clavicular fracture (~0.5–4%) ^[1]^[2]

Aspect	Detail
Mechanism	Direct pressure on the humerus during delivery of the posterior arm (the arm is flexed at the elbow and swept across the chest — if the bone is fragile or the manoeuvre is forceful, the humerus can fracture). Can also occur from compression between the baby and the maternal pelvis
Clinical features	Pseudoparalysis; swelling of the arm; crepitus; angulation
Investigation	X-ray of the humerus — typically a spiral or transverse mid-shaft fracture
Management	Immobilisation with the arm bandaged to the trunk. Neonatal humeral fractures heal rapidly (2–4 weeks) with excellent remodelling
Prognosis	Excellent — full recovery with no long-term consequences in virtually all cases

The most devastating complication of shoulder dystocia. ^[1]^[2]

Aspect	Detail
Incidence	Approximately 0.5–3% of shoulder dystocia cases result in moderate-to-severe HIE
Mechanism	During shoulder impaction: (1) Umbilical cord compression between the fetal body and the pelvis stops placental gas exchange; (2) Thoracic compression prevents the delivered head from ventilating (the thorax cannot expand to allow breathing). Together, these cause progressive fetal hypoxia and metabolic acidosis. The pH drops ~0.04 units/minute. If unresolved within 4–8 minutes, irreversible neuronal injury occurs
Clinical features	Low Apgar scores; poor tone; seizures in first 24–72 hours; encephalopathy (altered consciousness, abnormal reflexes, feeding difficulties)
Grading (Sarnat staging)	Stage 1 (Mild): hyperalert, normal tone, no seizures → good prognosis. Stage 2 (Moderate): lethargy, hypotonia, seizures → variable. Stage 3 (Severe): coma, flaccid, absent reflexes → poor prognosis
Investigation	Paired cord blood gas (pH < 7.0, BE < -12); amplitude-integrated EEG (aEEG); MRI brain (at day 3–5 for extent of injury)
Management	Therapeutic hypothermia (cooling to 33.5°C for 72 hours) if criteria met (initiated within 6 hours of birth). Supportive NICU care. Anti-seizure medications (phenobarbitone first-line)
Long-term consequences	Cerebral palsy, developmental delay, epilepsy, cognitive impairment, death

Time = Brain

The relationship between head-to-body delivery interval and HIE is approximately linear: every additional minute of impaction deepens the acidosis by ~0.04 pH units. This is why structured drills that minimise time to delivery are the most important factor in preventing HIE. ^[1]^[2]

Aspect	Detail
Incidence	Rare but devastating — approximately 0.02–0.05% of shoulder dystocia cases
Mechanism	Prolonged total cord occlusion + inability to ventilate → irreversible cardiac arrest from profound hypoxia and acidosis
Risk factors for death	Prolonged head-to-body interval (> 5–8 minutes); bilateral shoulder impaction; failure of all manoeuvres; delayed recognition

In babies born to diabetic mothers (the most common predisposing factor for shoulder dystocia), metabolic complications are especially relevant: ^[8]

Complication	Mechanism	Management
Neonatal hypoglycaemia ^[8]	Fetal hyperinsulinism (in response to chronic maternal hyperglycaemia in utero) persists after delivery when the placental glucose supply is suddenly cut off. The high insulin drives blood glucose down rapidly	Serial blood glucose monitoring (at 1, 2, 4, 8, 12, 24h); early feeding; IV dextrose if severe (< 2.0 mmol/L) or symptomatic
Polycythaemia	Chronic fetal hypoxia in utero (in poorly controlled diabetes) stimulates erythropoietin → increased RBC mass	Monitor haematocrit; partial exchange transfusion if symptomatic and haematocrit > 65%
Hypocalcaemia	Associated with infants of diabetic mothers; mechanism incompletely understood (possibly related to functional hypoparathyroidism)	Monitor calcium levels; IV calcium gluconate if symptomatic
Hyperbilirubinaemia / jaundice ^[8]	(1) Polycythaemia → more RBCs to break down → more bilirubin; (2) Birth trauma (bruising, haematomas) → haemoglobin released → bilirubin production; (3) Hepatic immaturity (especially if preterm)	Phototherapy; monitor transcutaneous/serum bilirubin
Respiratory complications ^[8]	(1) TTN (transient tachypnoea of the newborn) — more common after CS; (2) RDS — surfactant deficiency, more common if preterm or if delivery was expedited before lung maturity; (3) Aspiration if asphyxia occurred during impaction	Respiratory support as needed; surfactant if RDS

2. Maternal Complications

Aspect	Detail
Incidence	Increased significantly after shoulder dystocia (~11% vs ~5% in normal deliveries)
Mechanism	Two pathways: (1) Uterine atony — prolonged and traumatic labour exhausts the myometrium, which fails to contract adequately after delivery (the uterus is "tired"). Atony is the most common cause of PPH in any delivery. (2) Genital tract trauma — episiotomy, cervical lacerations, vaginal wall tears from internal manoeuvres (Rubin II, Wood's screw, posterior arm delivery)
Management	Active management of third stage (oxytocin 10 IU IM); bimanual uterine compression; uterotonics (ergometrine, carboprost, misoprostol) if atony persists; repair of lacerations; tranexamic acid 1g IV if PPH; blood transfusion if haemodynamically compromised

Type	Mechanism	Detail
3rd degree tear	Extension of episiotomy or spontaneous tear involving the anal sphincter	Occurs in ~3.8% of shoulder dystocia deliveries (vs ~1% in normal deliveries). Internal manoeuvres and urgency of the situation increase the risk
4th degree tear	Tear extends through the anal sphincter AND rectal mucosa	Rarer but more significant. Requires repair in theatre by an experienced surgeon
Cervical laceration	Internal manoeuvres (hands inserted past the cervix) or vigorous delivery	Always inspect the cervix post-delivery
Vaginal wall lacerations	Internal rotation manoeuvres; delivery of posterior arm	Inspect the vaginal walls systematically
Management	Systematic inspection under adequate anaesthesia; primary repair of all tears; 3rd/4th degree tears repaired in theatre; follow-up with perineal clinic; endoanal ultrasound if concern about incomplete repair

Aspect	Detail
Mechanism	The bladder and urethra sit immediately behind the pubic symphysis. During shoulder dystocia, the impacted shoulder compresses these structures. Symphysiotomy (if performed) carries specific risk of urethral injury
Clinical features	Haematuria, urinary retention post-delivery, suprapubic pain
Management	Catheterisation; monitor urine output; urology referral if significant injury

Aspect	Detail
Mechanism	Rare but catastrophic. Can occur from: (1) Fundal pressure (which is contraindicated — pushes the fetus against the impacted shoulder and the thinned lower uterine segment); (2) Zavanelli manoeuvre (forceful replacement of the head); (3) Excessive force during internal manoeuvres in a scarred uterus
Clinical features	Sudden cessation of contractions; abdominal pain; maternal tachycardia and hypotension; fetal bradycardia; palpable fetal parts abdominally
Management	Emergency laparotomy; repair or hysterectomy depending on extent

Aspect	Detail
Incidence	Significantly underrecognised; affects up to 30–50% of mothers who experience shoulder dystocia
Types	Post-traumatic stress disorder (PTSD): flashbacks, nightmares, hypervigilance, avoidance of anything related to childbirth. Postnatal depression: low mood, anhedonia, poor bonding. Anxiety disorders: especially tokophobia (fear of future childbirth)
Mechanism	The emergency, the feeling of helplessness, the fear for the baby's life, the pain of manoeuvres, and any adverse neonatal outcome (BPI, fractures) all contribute to psychological trauma
Management	Debrief with the mother and partner as soon as possible after the event (explain what happened and why). Follow-up at 6 weeks with psychological screening (Edinburgh Postnatal Depression Scale, PCL-5 for PTSD). Referral to perinatal mental health services if needed. Counselling about future pregnancy options
Impact on future pregnancies	May cause significant anxiety and tokophobia; can influence decision-making about mode of delivery (many women request elective CS after previous shoulder dystocia)

Don't Forget the Mother's Mental Health

In the aftermath of shoulder dystocia, clinicians often focus entirely on the neonatal outcome and forget about the mother's psychological wellbeing. Always debrief, screen, and follow up. Shoulder dystocia is one of the most psychologically traumatic birth experiences for both mothers and clinicians. ^[1]^[2]

Aspect	Detail
Mechanism	Excessive twisting or traction forces applied to the fetal head can theoretically injure the fetal cervical spine. Also, maternal cervical spine strain from McRoberts (extreme hip flexion) is theoretically possible but unreported
Incidence	Extremely rare
Prevention	Avoid excessive or uncontrolled traction; follow structured manoeuvres

Complication	Detail	Prognosis
Permanent Erb palsy	~10–20% of BPI cases do not recover fully; residual weakness in shoulder abduction, elbow flexion, forearm supination	May require surgical nerve reconstruction, tendon transfers, or adaptive devices
Cerebral palsy	Secondary to HIE from prolonged impaction	Lifelong; severity depends on extent of brain injury
Epilepsy	Secondary to HIE	May require long-term anti-epileptic medication
Developmental delay / intellectual disability	Secondary to HIE	Variable; depends on severity
Maternal chronic pelvic floor dysfunction	From perineal trauma (3rd/4th degree tears) and pelvic floor injury	Anal incontinence, urinary incontinence, pelvic organ prolapse in later life
Medicolegal consequences	Shoulder dystocia is one of the most litigated obstetric events worldwide	Robust documentation, structured drills, and informed consent are protective

Category	Complication	Incidence	Mechanism	Prognosis
Neonatal — Nerve	Erb palsy (C5–C6)	2.3–16%	Lateral stretch of upper brachial plexus	80–90% spontaneous recovery
Neonatal — Nerve	Klumpke palsy (C8–T1)	Rare	Upward traction on arm stretching lower trunk	Poorer; avulsion risk
Neonatal — Nerve	Total plexus palsy	Rare	Severe stretch/avulsion C5–T1	Worst; needs surgery
Neonatal — Bone	Clavicular fracture	2–10%	Compression against symphysis	Excellent — heals in 2–3 weeks
Neonatal — Bone	Humeral fracture	0.5–4%	Force during posterior arm delivery	Excellent — heals in 2–4 weeks
Neonatal — CNS	HIE	0.5–3%	Cord compression + thoracic compression → hypoxia	Variable — depends on duration
Neonatal — Death	Stillbirth / neonatal death	0.02–0.05%	Prolonged total asphyxia	Fatal
Neonatal — Metabolic	Hypoglycaemia, jaundice, polycythaemia	Variable	Diabetic-mother-related hyperinsulinism; birth trauma	Treatable
Maternal	PPH	~11%	Uterine atony + genital tract lacerations	Treatable
Maternal	3rd/4th degree tear	~3.8%	Mechanical trauma from manoeuvres	Repairable; risk of long-term incontinence
Maternal	PTSD / postnatal depression	Up to 30–50%	Psychological trauma of emergency	Needs screening and treatment
Maternal	Uterine rupture	Very rare	Fundal pressure or Zavanelli	Life-threatening

High Yield Summary — Complications of Shoulder Dystocia

Brachial plexus injury is the signature complication: most commonly Erb palsy (C5–C6, "waiter's tip"); 80–90% recover spontaneously (neuropraxia); permanent injury in 10–20% ^[1]^[2]
BPI can occur from endogenous forces (maternal pushing/contractions) without clinician traction — important medicolegal point
Clavicular fracture is the most common fracture (~2–10%); heals in 2–3 weeks; excellent prognosis
HIE is the most devastating complication — caused by cord compression + inability to ventilate; pH drops ~0.04/min; irreversible brain injury in 4–8 minutes; therapeutic hypothermia if criteria met
PPH occurs in ~11% — from uterine atony (exhausted myometrium) and genital tract lacerations
3rd/4th degree perineal tears occur in ~3.8% — from emergency manoeuvres
Maternal PTSD/depression affects up to 30–50% — always debrief, screen, and follow up
Neonatal metabolic complications (hypoglycaemia, jaundice, polycythaemia) are especially relevant in babies of diabetic mothers ^[8]
Two things that worsen complications: excessive lateral traction (→ BPI) and fundal pressure (→ worsened impaction, uterine rupture) — BOTH ARE CONTRAINDICATED ^[1]^[2]
Documentation is critical — shoulder dystocia is one of the most litigated obstetric events

Active Recall - Complications of Shoulder Dystocia

^[1] Lecture slides: Block C - Obstetric Emergency Notes to Students.pdf ^[2] Lecture slides: OBGYN Clinical Test By Topic.pdf ^[8] Lecture slides: GC 115. I am pregnant medical problems complicating pregnancy.pdf

High Yield Summary

Shoulder Dystocia — Key Points for Exams

Definition: Need for additional obstetric manoeuvres after gentle downward traction fails to deliver the shoulders, OR head-to-body interval > 60 seconds
Incidence: ~0.6–1.4% of vaginal cephalic deliveries
Mechanism: Anterior shoulder impacted behind pubic symphysis; bisacromial diameter > AP diameter of pelvic inlet
Risk factors: Fetal macrosomia (especially diabetic macrosomia), GDM, maternal obesity, previous shoulder dystocia, prolonged labour, instrumental delivery — but ~50% are UNPREDICTABLE
Key sign: Turtle sign — head delivers then retracts against the perineum
Time-critical: Irreversible brain injury within 4–8 minutes; cord pH drops ~0.04/min
Diabetic vs constitutional macrosomia: Diabetic macrosomia is DISPROPORTIONATE (trunk > head) → higher risk of shoulder dystocia at any given weight
Brachial plexus injury: Most commonly Erb palsy (C5–C6); can occur from clinician traction OR endogenous forces
Cannot be reliably predicted or prevented → ALL birth attendants must be trained in management drills

High Yield Summary — Differential Diagnosis of Shoulder Dystocia

Most common cause of failure to deliver the body after the head: true anterior shoulder dystocia (anterior shoulder behind pubic symphysis)
Key diagnostic feature: Turtle sign + failure of gentle downward traction + need for additional manoeuvres
"Tight shoulders" ≠ shoulder dystocia — no special manoeuvres needed = not shoulder dystocia
Must differentiate from: short/nuchal cord (tethering, not bony impaction), posterior shoulder dystocia (posterior on sacral promontory — suprapubic pressure won't help), bilateral impaction (both shoulders above inlet — worst scenario), fetal anomaly causing body obstruction, locked twins, cervical constriction ring
~50% of cases are unpredictable — universal preparedness > selective prediction
Highest-risk scenario: diabetic macrosomia + instrumental delivery + prolonged second stage
Murtagh's safe diagnostic model: probability diagnosis (true SD), can't miss (bilateral impaction, cord complications), pitfalls (tight shoulders misclassified), masquerade (short cord, fetal anomaly) ^[5]

High Yield Summary — Diagnostic Criteria, Algorithm & Investigations

Diagnosis is CLINICAL and made in REAL-TIME: turtle sign + failure of gentle downward traction + need for additional obstetric manoeuvres (or head-to-body interval > 60 seconds)
No blood test, imaging, or scoring system diagnoses shoulder dystocia — it is an intrapartum event
Antepartum investigations (USS for EFW, OGTT for GDM) are for RISK STRATIFICATION only — they cannot predict shoulder dystocia reliably (PPV < 30%)
USS EFW has ±10-15% error — this is why routine CS for suspected macrosomia alone is not recommended
~50% of cases occur without identifiable risk factors → universal preparedness over selective prediction
Post-event investigations focus on complications:
- Neonate: Paired cord blood gas (most important), Apgar, neurological exam (brachial plexus), skeletal assessment (clavicle/humerus fracture), blood glucose
- Mother: Genital tract inspection (tears), blood loss assessment, coagulation screen if PPH, psychological screening
Paired cord blood gas must be taken within 60 minutes; arterial pH < 7.0 and/or base excess < -12 indicates significant acidosis
Documentation is crucial — record timeline, manoeuvres (in sequence), personnel, outcomes; use structured proforma

High Yield Summary — Management of Shoulder Dystocia

HELPERR mnemonic is the standard management algorithm — must know each step, the mechanism, and the sequence ^[1]^[2]
McRoberts + suprapubic pressure resolves ~40–50% of cases — always start here (first-line, safest, fastest)
Posterior arm delivery has the highest individual success rate (~85%) — reduces bisacromial diameter by ~20%
NEVER apply excessive lateral traction (causes brachial plexus injury) or fundal pressure (worsens impaction) ^[1]^[2]
Episiotomy does NOT relieve bony obstruction but creates space for internal manoeuvres
Gaskin manoeuvre (all-fours) uses gravity and changes pelvic diameters but is limited by epidural anaesthesia
Last-resort manoeuvres: Zavanelli (cephalic replacement → emergency CS), symphysiotomy, deliberate clavicular fracture
Post-event: cord gases, neonatal exam (brachial plexus, fractures, glucose), maternal assessment (tears, PPH, psychology), structured documentation, future pregnancy counselling
Shoulder dystocia is a recognised intrapartum risk factor for anticipation of neonatal resuscitation ^[7]
~50% of cases are unpredictable → ALL birth attendants must be trained through simulation drills

High Yield Summary — Complications of Shoulder Dystocia

Brachial plexus injury is the signature complication: most commonly Erb palsy (C5–C6, "waiter's tip"); 80–90% recover spontaneously (neuropraxia); permanent injury in 10–20% ^[1]^[2]
BPI can occur from endogenous forces (maternal pushing/contractions) without clinician traction — important medicolegal point
Clavicular fracture is the most common fracture (~2–10%); heals in 2–3 weeks; excellent prognosis
HIE is the most devastating complication — caused by cord compression + inability to ventilate; pH drops ~0.04/min; irreversible brain injury in 4–8 minutes; therapeutic hypothermia if criteria met
PPH occurs in ~11% — from uterine atony (exhausted myometrium) and genital tract lacerations
3rd/4th degree perineal tears occur in ~3.8% — from emergency manoeuvres
Maternal PTSD/depression affects up to 30–50% — always debrief, screen, and follow up
Neonatal metabolic complications (hypoglycaemia, jaundice, polycythaemia) are especially relevant in babies of diabetic mothers ^[8]
Two things that worsen complications: excessive lateral traction (→ BPI) and fundal pressure (→ worsened impaction, uterine rupture) — BOTH ARE CONTRAINDICATED ^[1]^[2]
Documentation is critical — shoulder dystocia is one of the most litigated obstetric events

Shoulder Dystocia

1. Definition

2. Epidemiology

3. Anatomy & Function

3.1 Relevant Maternal Pelvic Anatomy

3.2 Relevant Fetal Anatomy

3.3 Brachial Plexus Anatomy (Critical for Understanding Complications)

4. Risk Factors

4.1 Antepartum (Pre-Labour) Risk Factors

4.2 Intrapartum Risk Factors

5. Aetiology & Pathophysiology

5.1 Aetiology (Hong Kong Focus)

5.2 Pathophysiology — Step-by-Step Mechanism

5.3 Pathophysiology of Associated Complications

6. Classification

6.1 By Severity of Impaction

6.2 By Clinical Recognition

6.3 By Outcome Severity

7. Clinical Features

7.1 Symptoms (What the Mother/Birth Attendant Experiences)

7.2 Signs (What the Clinician Observes)

7.3 Signs Specific to Complications (Identified After Delivery)

7.4 Timeline of Clinical Features

8. Connecting Clinical Features to Pathophysiology — Summary Table

Active Recall - Shoulder Dystocia (Definition, Epidemiology, Risk Factors, Anatomy, Pathophysiology, Clinical Features)

References

Why a "Differential Diagnosis" Section for Shoulder Dystocia?

Applying Murtagh's Safe Diagnostic Model [5]

Differential Diagnosis Table

Clinical Decision-Making Flowchart

Key Differentiating Points: True Shoulder Dystocia vs Mimics

True Shoulder Dystocia vs Tight Shoulders

True Shoulder Dystocia vs Short/Nuchal Cord

True Shoulder Dystocia vs Posterior Shoulder Impaction

Conditions That Predispose to Shoulder Dystocia (Differential for "Why Did This Happen?")

Red Flags During Labour That Should Heighten Suspicion

Summary of Differential Diagnosis Approach

Active Recall - Differential Diagnosis of Shoulder Dystocia

Diagnostic Criteria, Diagnostic Algorithm & Investigations for Shoulder Dystocia

1. Diagnostic Criteria

1.1 Clinical Diagnostic Criteria (At the Time of Delivery)

1.2 Recognition Features (How You Know It Is Happening)

1.3 What Does NOT Constitute Shoulder Dystocia

2. Diagnostic Algorithm

2.1 Pre-Delivery: Risk Assessment (Antepartum & Intrapartum)

Antepartum Risk Assessment

Intrapartum Warning Signs

2.2 At the Moment of Delivery: Recognition Algorithm

2.3 Post-Delivery: Confirming and Documenting the Diagnosis

3. Investigations

3.1 Key Principle: Shoulder Dystocia Is a Clinical Diagnosis — Investigations Are Post-Event

3.2 Antepartum Investigations (Risk Stratification — NOT Diagnostic)

3.3 Intrapartum Investigations (During Labour)

3.4 Post-Event Investigations (After Delivery)

3.4.1 Neonatal Investigations

3.4.2 Maternal Investigations

3.5 Summary Table — Investigation Modalities by Timing

3.6 Interpreting Cord Blood Gas — A Critical Skill

4. Complete Diagnostic & Investigation Algorithm

Active Recall - Diagnostic Criteria, Algorithm & Investigations for Shoulder Dystocia

References

Management of Shoulder Dystocia

1. Preparation and Prevention

1.1 Antepartum Counselling and Planning

1.2 Intrapartum Preparedness

2. The HELPERR Mnemonic — Systematic Management Algorithm

3. Detailed Explanation of Each HELPERR Step

H — Call for Help

E — Evaluate for Episiotomy

L — Legs: McRoberts Manoeuvre

P — Suprapubic Pressure

E — Enter: Internal Manoeuvres (Rubin II and Wood's Screw)

Rubin II Manoeuvre

Wood's Screw Manoeuvre

Combined Rubin II + Wood's Screw

R — Remove the Posterior Arm

R — Roll the Patient: Gaskin Manoeuvre (All-Fours Position)

4. Last-Resort Manoeuvres

4.1 Zavanelli Manoeuvre (Cephalic Replacement)

4.2 Symphysiotomy