CFB OGPAE01-1 Perinatal Medicine, Antenatal Care And Pre-pregnant Counselling (part I)
Perinatal medicine and antenatal care encompass the systematic medical supervision of pregnancy from preconception counseling through the prenatal period, including risk assessment, health optimization, and screening to ensure optimal maternal and fetal outcomes.
Antenatal Care & Pre-Pregnancy Counselling (Part I)
Big Idea: The goal of antenatal care is captured in four words — "Healthy mother and healthy baby." [1] Everything in this lecture flows from that objective. Antenatal care is a systematic programme of screening, prevention, education, and early detection of problems in both mother and fetus, ideally starting before conception with pre-pregnancy counselling and continuing through a structured visit schedule until delivery.
Learning Objectives (from the lecture):
- Understand the three pillars of antenatal care: prevention, screening (early detection), and education [1]
- Know what maternal and fetal conditions we screen for, how we screen, and when
- Understand thalassaemia screening workflow in detail
- Know the Down syndrome screening pathway (first tier → second tier → diagnostic)
- Understand principles of fetal growth assessment, gestational age estimation, lie/presentation
- Appreciate the principles of pre-pregnancy counselling for women with medical diseases
How it fits into exams: This is a bread-and-butter O&G lecture. Past papers repeatedly test antenatal screening investigations (which test for which condition), thalassaemia screening algorithm, Down syndrome screening methods, gestational hypertension definitions, and GDM screening. Expect MCQs asking "most appropriate investigation" and SAQs on screening algorithms.
Why Antenatal Care Exists
Pregnancy is a physiological state, but it creates unique risks. The maternal cardiovascular system undergoes massive changes (blood volume increases ~40%, cardiac output rises, SVR falls), the immune system is modulated, and the fetus is developing rapidly with windows of vulnerability. Many complications (pre-eclampsia, GDM, fetal anomalies, malpresentation) are silent until they become dangerous. Antenatal care is the structured opportunity to catch these problems early when intervention can change outcomes.
The three objectives of antenatal care: (1) Prevention of abnormalities, (2) Early detection of abnormalities (screening), (3) Education. [1]
Slide-by-Slide High-Yield Content
The lecture repeatedly returns to this framework. Every screening topic falls under either maternal or fetal categories [1]:
| Maternal | Fetal |
|---|---|
| General health including anaemia | Incorrect gestational age |
| Common infections | Multiple pregnancy |
| Pregnancy complications: GDM, hypertension | Congenital abnormalities |
| Abnormal growth | |
| Abnormal lie and presentation |
Screening tools: History (past health, past OB Hx, age, family Hx, habits, menstrual Hx, symptoms), Physical examination (weight, height, general, BP, urinalysis, uterine size), Investigations (Hb, HBsAg, Rubella, Rh, VDRL, HIV, ultrasound), Specific screening programs (Down syndrome, thalassaemia). [1]
High Yield – Booking Investigations
The "booking bloods" you must know: Hb, HBsAg, Rubella antibody, Rh blood group, VDRL, HIV, MCV (for thalassaemia screening). These are tested routinely at the first antenatal visit. Ultrasound for dating is also standard at booking.
Hb is checked at booking AND at 26 weeks. Why repeat? Because iron demands increase dramatically in the second half of pregnancy (fetal growth, expanding maternal blood volume, placental needs), so a woman who was borderline at booking may become frankly anaemic by 26 weeks. [1]
Causes of anaemia in pregnancy:
- Iron deficiency — most common; from chronic blood loss (e.g. menorrhagia pre-pregnancy), inadequate dietary intake, or increased demands of pregnancy
- Thalassaemia — especially relevant in HK Chinese population
- Other rarer causes — folate deficiency, B12 deficiency, haemolysis
Why it matters: Maternal anaemia is associated with preterm delivery, low birth weight, and poor maternal recovery postpartum. Severe anaemia increases risk of postpartum haemorrhage complications.
Physical sign: Pallor (conjunctival, palmar creases, nail beds)
Investigation approach: Once anaemia is confirmed, determine the cause:
- Check MCV → microcytic suggests iron deficiency or thalassaemia
- Iron studies (serum ferritin) → low ferritin = iron deficiency
- Hb pattern (Hb electrophoresis) → identifies thalassaemia type
This is one of the highest-yield topics from this lecture. It has appeared in multiple past papers [7][8].
Screening test: MCV. Cut-off: < 82 fL. [1]
Why MCV? Thalassaemia causes microcytosis because there is reduced globin chain production → smaller, more hypochromic red cells. MCV is a cheap, universally available screening tool.
Why 82 fL specifically? This is the HK protocol cut-off, chosen to maximise sensitivity for catching thalassaemia carriers in the local population. Note: some sources previously used 80 fL, but HKU/QMH uses 82 fL [1][6].
Thalassaemia Screening Algorithm
| Step | Action | Rationale |
|---|---|---|
| 1 | Check MCV of pregnant woman at booking | Screening test |
| 2 | If MCV < 82 fL → Check Hb pattern (electrophoresis) + check ferritin | Need to determine whether microcytosis is from thalassaemia or iron deficiency |
| 3a | High HbA2 → Beta-thalassaemia trait | Beta-thal carriers have elevated HbA2 (normally ~2.5%, elevated > 3.5%) because when beta chains are reduced, delta chains are relatively overproduced |
| 3b | HbH inclusions on peripheral smear → Alpha-thalassaemia trait | HbH = β4 tetramers; form when alpha chains are deficient |
| 3c | Normal Hb pattern → Check ferritin | If ferritin low → iron deficiency causing the low MCV. If ferritin normal, consider silent alpha-thal carrier (1 gene deletion — may not show HbH) |
| 4 | If woman is a carrier → Test partner's MCV | Need to know if couple is at risk of having affected offspring |
| 5 | If both partners are carriers → Genetic counselling + prenatal diagnosis | Risk of homozygous disease (e.g. Hb Bart's hydrops fetalis for alpha-thal, beta-thal major) |
Critical Exam Trap — Mixed Alpha + Beta Thal
A person can carry BOTH alpha AND beta thalassaemia genes simultaneously. Alpha-thal carriers do NOT always show HbH inclusions on peripheral smear. Therefore, if one partner has beta-thal, the beta-thal partner should have DNA testing to EXCLUDE coexisting alpha-thal gene deletion. [1] This is a favourite exam pitfall — the question might present a couple where one is beta-thal and the other is alpha-thal, and ask about the risk of Hb Bart's hydrops fetalis.
Epidemiology in HK Chinese (from supporting material):
- ~5% are alpha-thal carriers (with low MCV)
- ~3% are beta-thal carriers
- ~0.3% have HbE
- ~3% have very mild alpha-thal (1 gene deletion, normal MCV)
- Total: ~11.3% of HK Chinese are carriers of some form of thalassaemia [5]
This is why universal screening is so important in our population.
Routine infection screening: HBsAg, Syphilis (VDRL), HIV, Group B Streptococcus (GBS — low vaginal swab and rectal swab). [1]
| Infection | Test | Timing | Why Screen |
|---|---|---|---|
| Hepatitis B | HBsAg | Booking | Vertical transmission → neonatal hepatitis, chronic carrier state. If positive, baby gets HBIg + HBV vaccine within 24h of birth [8] |
| Syphilis | VDRL | Booking | Congenital syphilis causes stillbirth, hydrops, bone/teeth/neurological defects. Treatable with penicillin |
| HIV | HIV antibody | Booking | Without intervention, MTCT rate ~25-30%. With cART + elective CS if high viral load, rate drops to < 1% |
| GBS | Low vaginal + rectal swab | 35-37 weeks | GBS is the leading cause of early-onset neonatal sepsis. If positive, give IV benzylpenicillin in labour [9] |
| Rubella | Rubella IgG antibody | Booking | Check immunity. If non-immune → vaccinate postpartum (live vaccine, cannot give in pregnancy). Rubella in 1st trimester causes congenital rubella syndrome (deafness, cataracts, cardiac defects) |
STD screening is indicated when: high-risk history (multiple sexual partners, previous STD history), or when positive for one STD (screen for others). [1]
Other tests when indicated:
- Increased vaginal discharge → vaginal swab
- Proteinuria → differentiate from vaginal contamination; send MSU for UTI
Strategy: Risk factor identification + universal OGTT. [1]
Risk factors for early OGTT (between booking and 16 weeks):
| Category | Risk Factors |
|---|---|
| Maternal | Obesity, age ≥ 35 years, PCOS, family history of DM |
| Past OB history | Previous babies > 4 kg, previous unexplained stillbirth, abnormal babies not related to known chromosomal/genetic abnormalities |
| Current pregnancy | Multiple pregnancy |
Women WITH risk factors → Early 75g OGTT (between booking and 16 weeks). Women WITHOUT risk factors → Routine 75g OGTT at 26-32 weeks. [1]
Why screen? GDM causes macrosomia (shoulder dystocia, birth trauma), neonatal hypoglycaemia, neonatal polycythaemia, and increases risk of pre-eclampsia. Long-term, GDM mothers have higher risk of developing type 2 DM.
Why 75g OGTT? This is the gold standard diagnostic test. In HK, we use universal screening (every pregnant woman gets an OGTT) rather than selective screening, because risk factors alone miss a significant proportion of GDM cases.
Past Paper Pattern — OGTT Timing
A past paper MCQ (2020) presented a 25-year-old woman at 12 weeks with family history of DM in her mother, asking for the most appropriate investigation. The answer is 75g OGTT (early OGTT, because she has a family history of DM — a risk factor). Do NOT answer "random blood glucose" or "HbA1c" — the OGTT is the standard test in pregnancy [4].
Baseline BP at first visit (ideally before 20 weeks) — if elevated, likely pre-existing hypertension. BP at every subsequent antenatal visit. [1]
Gestational hypertension = two readings of BP ≥ 140 mmHg systolic, or ≥ 90 mmHg diastolic, more than 4 hours apart, after 20 weeks of gestation, in a woman with previously normal BP. [1]
Key definitions:
| Condition | Definition |
|---|---|
| Pre-existing (chronic) HT | HT present before pregnancy or detected before 20 weeks |
| Gestational HT | New HT after 20 weeks, no proteinuria, no end-organ damage |
| Pre-eclampsia | HT after 20 weeks + proteinuria (≥ 2+ on dipstick) ± end-organ dysfunction |
| Superimposed pre-eclampsia | Pre-existing HT + new proteinuria or worsening HT after 20 weeks |
Urine for albumin is checked at every visit. Pre-eclampsia = gestational HT + proteinuria. [1]
Why does the 20-week threshold matter? The pathology of pre-eclampsia begins in the first trimester with abnormal trophoblast invasion of spiral arteries, but the clinical syndrome manifests after 20 weeks. Any hypertension detected before 20 weeks is almost certainly pre-existing, not pregnancy-induced.
Past Paper Favourite — Distinguishing HT Types in Pregnancy
A 2023 MCQ presented a 20-year-old G2P0 with good past health, normal BP at 12 weeks, now with BP 150/100 at 34 weeks and urine albumin 3+. The answer is Pre-eclampsia (NOT gestational HT — because there IS proteinuria; NOT chronic HT — because BP was normal at 12 weeks) [10].
8. Fetal Screening — Estimation of Gestational Age
Why accurate dating matters: Almost every obstetric decision depends on knowing the gestational age — screening test timing, expected milestones, when to induce, whether growth is appropriate.
Based on LMP, assuming ovulation occurring 14 days after LMP (1st day). This assumption is NOT true if: unsure LMP, long or irregular cycles, recent use of hormonal contraception. [1]
Naegele's Rule (not explicitly on slides but essential background): EDD = LMP − 3 months + 7 days + 1 year. This only works for a regular 28-day cycle.
In a singleton pregnancy, the gravid uterine size corresponds to gestational age. SFH in cm ≈ gestation in weeks (±2). [1]
The fundus is palpable:
- 12 weeks — just above the pubic symphysis
- 20 weeks — at the umbilicus
- 36 weeks — at the xiphisternum (then may plateau or drop as head engages)
Clinical estimation can be affected by: number of fetuses, liquor volume, presence of fibroids, abdominal wall thickness, lie of fetus, descent into pelvis. [1]
This is the most accurate method, but accuracy deteriorates with advancing gestation:
| Gestation | Accuracy | Parameter Used |
|---|---|---|
| < 12 weeks | ± 4-5 days | Crown-rump length (CRL) |
| 13-14 weeks | ± 1 week | CRL or biparietal diameter (BPD) |
| 14-20 weeks | ± 10 days | BPD, head circumference (HC), femur length (FL) |
| 20-24 weeks | ± 2 weeks | BPD, HC, FL, abdominal circumference (AC) |
| > 24 weeks | Inaccurate | Normal biological variation + abnormal growth confound estimation |
After 24 weeks, increased normal biological variation and occurrence of abnormal growth make estimation of gestational age inaccurate. [1]
Clinical pearl: This is why the dating scan should ideally be done in the first trimester. If a woman books late, you cannot reliably date the pregnancy by ultrasound.
Clues from History: ovulation induction, assisted reproduction, maternal family history (dizygotic twins run in families on the maternal side), exaggerated symptoms of pregnancy (worse nausea/vomiting from higher hCG). [1]
Physical examination: uterus larger than dates, multiple fetal poles, multiple fetal heart sounds. [1]
Ultrasound examination — earliest and most reliable method for detecting multiple pregnancy. [1]
Why it matters: Multiple pregnancy carries higher risk of preterm delivery, pre-eclampsia, GDM, fetal growth restriction, twin-to-twin transfusion syndrome (in monochorionic twins), malpresentation, and PPH.
Key point on chorionicity: Determining chorionicity (monochorionic vs dichorionic) is critical and is best done in the first trimester by looking for the "lambda sign" (dichorionic) vs "T-sign" (monochorionic) at the membrane-placenta junction.
Risk factors from history: family history, previous abnormal babies, advanced maternal age, teratogenic drugs or irradiation, infection. However, MOST abnormal babies are born to parents WITHOUT identifiable risk factors. [1]
This is a crucial concept — it justifies universal screening rather than selective screening based on risk factors alone.
Ultrasound examination at 18-20 weeks detects ~70% of major fetal abnormalities. Accuracy can be lower than 70% with increased BMI or unfavourable fetal position. [1]
Detection Rates by Anomaly Type (from lecture slides)
| Fetal Anomaly | Detection Rate |
|---|---|
| Anencephaly | 98% |
| Gastroschisis | 98% |
| Open spina bifida | 90% |
| Bilateral renal agenesis | 84% |
| Exomphalos (omphalocele) | 80% |
| Cleft lip | 75% |
| Hydrocephalus | 60% |
| Diaphragmatic hernia | 60% |
| Lethal skeletal dysplasia | 60% |
| Serious cardiac anomalies (TGA, AVSD, TOF, HLHS) | 50% |
Why Cardiac Anomalies Have Low Detection Rate
Congenital heart disease has only ~50% detection on anomaly scan because the four-chamber view (the standard screening view) can appear normal in conditions like TGA (where the chambers are normal but the great vessels are swapped) and TOF (where the ventricular septal defect may be subtle). This is why outflow tract views are important additions to the screening protocol, but even then, detection remains suboptimal.
11. Screening for Fetal Down Syndrome
This is a multi-tiered system. The lecture clearly outlines first tier → second tier → diagnostic tests [1].
| Screening Test | Gestation | Components | Detection Rate |
|---|---|---|---|
| First trimester combined screening | 11w – 13+6w | USG for nuchal translucency (NT) + blood for PAPP-A + hCG | ~90% |
| Second trimester quadruple screening | 14w – 19+6w | Blood for AFP, hCG, estriol (E3), inhibin-A | ~80% |
All women booked at the antenatal clinic will be offered Down Syndrome Screening (DSS) based on gestation at booking visit. [1]
Why first trimester screening is preferred:
- Higher detection rate (90% vs 80%)
- Earlier result → earlier decision-making
- NT measurement also identifies risk of other chromosomal abnormalities AND major structural anomalies (e.g. cardiac defects)
Abnormally high nuchal translucency is known to be associated with other chromosomal and congenital birth defects [1] — not just Down syndrome. Elevated NT is associated with Turner syndrome, trisomy 18, trisomy 13, cardiac defects, and other structural anomalies.
Maternal age and Down syndrome risk:
| Maternal Age at Delivery | Risk of Down Syndrome |
|---|---|
| All ages | 1:650 |
| 30 | 1:700 |
| 35 | 1:450 |
| 38 | 1:200 |
| 40 | 1:100 |
| 42 | 1:60 |
| 44 | 1:40 |
The risk of ALL chromosomal abnormalities increases with age. [1]
Why? Non-disjunction during meiosis is more likely to occur in oocytes that have been arrested in prophase I for decades. The longer the oocyte has been "sitting," the more likely the meiotic machinery deteriorates.
Past Paper — Down Syndrome Screening for Older Mother
A 2023 MCQ asked about DSS for a 42-year-old primigravida at 12 weeks. The answer is first trimester combined screening test [10]. Even though her age-related risk is already high (~1:60), she should still be offered the formal screening test first — not jumped straight to amniocentesis — because screening personalises her risk. If the screen is positive, THEN offer second-tier testing (NIPT or diagnostic).
If the first tier screening test is positive, counsel about second tier screening: (1) Non-Invasive Prenatal Test (NIPT), or (2) Diagnostic testing (CVS or amniocentesis). [1]
NIPT:
- Blood test based on cell-free fetal DNA (cfDNA) fragments in maternal plasma, originating from the placenta
- Detects 99.7% of trisomy 21 with ~0.1% false positive rate [1]
- Still a screening test, not diagnostic — must be confirmed by karyotyping if positive
- Can also screen for trisomy 18, trisomy 13, sex chromosome aneuploidies
| Test | Gestation | Procedure | Miscarriage Risk |
|---|---|---|---|
| Chorionic villus sampling (CVS) | 11-14 weeks | Needle through maternal abdominal wall + uterus into placenta under USG guidance → aspirate chorionic villi | 0.1-0.2% |
| Amniocentesis | 16-20 weeks | Needle through maternal abdominal wall + uterus + membranes into amniotic sac under USG guidance → aspirate amniotic fluid | 0.1-0.2% |
Key distinction: CVS samples placental tissue (chorionic villi), while amniocentesis samples amniotic fluid (containing fetal cells shed from skin, urinary tract, etc.). CVS can be done earlier, which is its main advantage. However, CVS carries a small risk of confined placental mosaicism (placental karyotype may differ from fetal karyotype).
Too small or too big? Does it matter? [1]
Yes — both extremes are associated with adverse outcomes.
Key distinctions:
- Small for Gestational Age (SGA) = birth weight < 10th centile for gestational age. A statistical definition. The baby might be constitutionally small (small parents) and perfectly healthy.
- Intrauterine Growth Restriction (IUGR) = pathological failure to reach genetic growth potential. Implies placental insufficiency or other pathology. These babies are at risk of fetal distress, stillbirth, neonatal hypoglycaemia, and long-term metabolic syndrome.
- Large for Gestational Age (LGA) = birth weight > 90th centile.
- Macrosomia = absolute birth weight > 4000g (or > 4500g by some definitions). Associated with GDM, shoulder dystocia, birth trauma.
Screening method: Clinical measurement of symphysio-fundal height (SFH). SFH in cm ≈ gestation in weeks (±2). Trend is more important than single measurements. Ultrasound is mainly for confirmation of clinical suspicion. Routine ultrasound to screen for fetal growth problems — effectiveness not proven. [1]
Clinical pearl: If the SFH is static or falling behind on serial measurements, that's more concerning than a single measurement that's slightly off. Always plot on a customised growth chart.
Fetal lie = the longitudinal axis of the fetus relative to the longitudinal axis of the uterus. [1]
| Lie | Description |
|---|---|
| Longitudinal | Fetal spine parallel to maternal spine (normal) |
| Transverse | Fetal spine perpendicular to maternal spine |
| Oblique | Fetal spine at an angle |
Fetal presentation = the part of the fetus that is presenting at the pelvic inlet. [1]
| Presentation | Part |
|---|---|
| Cephalic | Head (normal, ~96% at term) |
| Breech | Buttocks or feet (~3-4% at term) |
| Shoulder | Shoulder (in transverse lie) |
Before 32-34 weeks and not in labour — no clinical significance (fetus still has room to turn). Most fetuses will turn into longitudinal lie and cephalic presentation at 35-36 weeks. [1]
Breech presentation after 36 weeks → consider External Cephalic Version (ECV) if no contraindication. [1]
ECV: A procedure where the obstetrician manually rotates the baby from breech to cephalic through the maternal abdomen, guided by ultrasound. Done with tocolysis (e.g. terbutaline) to relax the uterus. Success rate ~50%. Contraindications include placenta praevia, multiple pregnancy, ruptured membranes, fetal compromise.
No, if the woman is already having regular screening. Yes, if the woman is NOT having regular screening — or advise postnatal screening (opportunistic screening). [1]
Why this matters: Pregnancy is often the most contact a young woman has with the healthcare system. It's an opportunity to catch women who have never had cervical screening. However, routine Pap smears are not part of standard antenatal care if the woman is up-to-date.
Three models: (1) Exclusive hospital (specialist) care — public or private; (2) Primary health care based with referral to specialist only when indicated — MCHC, midwife-led clinic; (3) Shared care between hospital and primary health care. [1]
In Hong Kong, the shared care system between Tsan Yuk Hospital (TYH), Queen Mary Hospital (QMH), and Maternal and Child Health Centres (MCHC) is used. Patients are risk-stratified (e.g. by modified McGill score): low-risk → shared care; high-risk → hospital-based care [3].
To be determined at 36 weeks in uncomplicated pregnancy. [1]
| Decision | Default |
|---|---|
| Timing | Allow spontaneous onset of labour at term (≥ 37 weeks). If maternal/fetal compromise → consider induction. Induction for post-term at ~41 weeks |
| Mode | Aim for vaginal delivery. Caesarean section if not fit for vaginal delivery |
Antenatal classes and exercises, contraceptive advice, family as a unit, social support network, special needs for abnormal pregnancies/babies, patient support groups. [1]
Important educational points (from supporting material):
- Diet: 2000-2500 kcal/day in last 2 trimesters, balanced with adequate protein
- Folic acid: 0.4 mg/day supplementation — prevents neural tube defects (should ideally start pre-conception and continue through the first trimester)
- Avoid alcohol, smoking, recreational drugs
- Safe medications: paracetamol is safe; NSAIDs contraindicated after 35 weeks (risk of premature closure of ductus arteriosus)
- Coitus generally safe unless: threatened miscarriage, PROM, placenta praevia, APH
18. Principles of Pre-Pregnancy Counselling
Women with pre-existing medical diseases (e.g. SLE, IDDM, epilepsy, congenital heart disease). [1]
The two key questions to address:
| Question | Why |
|---|---|
| How can the medical disease affect the pregnancy? | Maternal and fetal complications |
| How can the pregnancy affect the medical disease? | Disease may flare or progress |
Increased risk of: miscarriage, fetal growth restriction, preterm delivery, pre-eclampsia, neonatal lupus. Variable rates of SLE flares during pregnancy. [1]
Neonatal lupus occurs when anti-Ro/anti-La antibodies cross the placenta → can cause congenital heart block, rash, cytopenias. This is why a past paper asked about anti-Ro antibody testing in a fetus with complete heart block [9].
Adjustment of medications (switch to pregnancy-safe alternatives), recommended timing of conception (optimize medical disease before conception), contraceptive methods (until ready). [1]
| Medication Change | Rationale |
|---|---|
| Switch warfarin → LMWH | Warfarin is teratogenic (nasal hypoplasia, CNS defects in 1st trimester) |
| Switch ACEi/ARB → labetalol/nifedipine | ACEi/ARB cause renal agenesis, oligohydramnios |
| Switch methotrexate → azathioprine | Methotrexate is a folate antagonist — teratogenic and abortifacient |
| Continue hydroxychloroquine | Safe in pregnancy; reduces SLE flares |
| Optimise glycaemic control in DM (HbA1c < 6.5%) | High glucose in organogenesis → neural tube defects, cardiac defects |
This is a past-paper favourite that bridges physiology and clinical care.
From 2021 MCQ: A 36-year-old at 30 weeks with dizziness on changing posture, normal examination → answer is supine hypotension [11].
From 2023 SAQ: A 36-year-old at 28 weeks with dizziness in supine position → answer is supine hypotension [8].
Mechanism: The gravid uterus compresses the inferior vena cava when the woman lies supine, reducing venous return → reduced cardiac output → hypotension and dizziness. Worse in late second/third trimester as the uterus grows.
Management: Advise left lateral decubitus position; avoid lying flat; get up slowly.
Exam Intelligence
- "Most appropriate investigation" — Given a clinical scenario + gestation, pick the right test (OGTT vs MCV vs Hb pattern, etc.)
- Thalassaemia screening algorithm — Given MCV results, what's the next step?
- Down syndrome screening method — Given gestation, which tier of screening?
- Defining gestational HT vs pre-eclampsia vs chronic HT — Read the BP timing and proteinuria carefully
- GDM screening timing — Does this patient have risk factors? → Early vs routine OGTT
| Trap | Correct Approach |
|---|---|
| Confusing gestational HT with pre-eclampsia | Pre-eclampsia requires proteinuria or end-organ damage |
| Jumping to amniocentesis for DSS in advanced maternal age | Offer screening first (first trimester combined test), then second tier if positive |
| Forgetting that NIPT is still a screening test, not diagnostic | Even with 99.7% detection, a positive NIPT must be confirmed by CVS/amniocentesis |
| Using random blood glucose instead of OGTT for GDM | OGTT is the gold standard for diagnosis in pregnancy |
| Thinking alpha-thal always shows HbH inclusions | Alpha-thal carriers may have normal smear; DNA testing needed if partner has beta-thal |
-
MCQ: A 28-year-old at booking has MCV 75 fL. What is the most appropriate next investigation?
- Answer: Hb pattern (Hb electrophoresis) to differentiate iron deficiency from thalassaemia trait. Also check ferritin.
-
MCQ: A 35-year-old G1P0 at 11 weeks. What is the most appropriate Down syndrome screening?
- Answer: First trimester combined screening (NT + PAPP-A + hCG)
-
SAQ: A 35-year-old woman at 14 weeks has Hb 9.9 g/dL and MCV 80 fL. (a) What abnormalities? (b) Causes? (c) Further tests for the woman? (d) Investigation for husband? (e) Supplement? [7]
- Answer: (a) Anaemia + microcytosis; (b) Iron deficiency, thalassaemia trait; (c) Hb pattern + serum ferritin (or iron studies + DNA study); (d) MCV (CBC); (e) Iron supplement (and folic acid)
-
MCQ: Gestational HT is defined as BP ≥ / after ___ weeks, measured ___ hours apart, in a woman with previously ___ BP.
- Answer: ≥ 140/90 after 20 weeks, > 4 hours apart, previously normal BP
-
SAQ: A 40-year-old G1P0 at 39 weeks with BP 160/95 and urine protein 3+. (a) Most likely diagnosis? (b) Initial investigations? (c) Antihypertensive drugs?
- Answer: (a) Pre-eclampsia; (b) CBC, LFT, renal function, clotting, uric acid, urine PCR; (c) Labetalol, nifedipine, hydralazine [12]
High Yield Summary
Antenatal care = Prevention + Screening + Education.
Booking investigations: Hb, MCV, HBsAg, VDRL, HIV, Rubella Ab, Rh group, urinalysis, dating USG.
Thalassaemia screening: MCV < 82 fL → Hb pattern + ferritin → test partner if carrier → genetic counselling. Watch for mixed alpha + beta thal couples.
GDM screening: Risk factors → early 75g OGTT (booking–16w). No risk factors → routine 75g OGTT (26–32w).
Gestational HT: BP ≥ 140/90 after 20 weeks, > 4h apart. Add proteinuria → pre-eclampsia.
Down syndrome screening: 1st trimester (NT + PAPP-A + hCG, detects 90%) > 2nd trimester (quad screen, 80%). Screen positive → NIPT (99.7%) or diagnostic (CVS 11-14w / amnio 16-20w, miscarriage risk 0.1-0.2%).
Anomaly scan: 18-20 weeks, detects ~70% major anomalies. Cardiac anomalies only ~50%.
USG dating accuracy: Best < 12w (±4-5 days). After 24w → inaccurate.
SFH (cm) ≈ gestation (weeks) ±2. Trend matters more than single measurements.
Breech after 36 weeks → consider ECV.
Pre-pregnancy counselling: Assess bidirectional disease-pregnancy interaction. Switch to pregnancy-safe medications. Optimise disease control before conception.
Active Recall - Antenatal Care & Pre-Pregnancy Counselling (Part I)
[1] Lecture slides: CFB (OGPAE01-1) Perinatal Medicine, Antenatal Care and Pre-pregnant Counselling (Part I).pdf (slides 1-43) [2] Lecture slides: CFB (PAE01) Paediatric history taking.pdf (p4) [3] Senior notes: Adrian Lui Obstetric Notes.pdf (p17, p24) [4] Past papers: 2020 Fourth Summative Assessment MCQ paper.pdf (p36, Q6-7) [5] Senior notes: Block A - Many members of the family have anaemia.pdf (p10, p36) [6] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p589) [7] Past papers: 2025 Fourth Summative SAQ.pdf (p9, Q7) [8] Past papers: 2023 Fourth Summative SAQ.pdf (p3, Q2; p6, Q5) [9] Past papers: 2025 Fourth Summative MCQ.pdf (p29, Q75-76) [10] Past papers: 2023 Fourth Summative MCQ.pdf (p6, Q13-14) [11] Past papers: 2021 Fourth Summative Assessment MCQ.pdf (p4, Q9) [12] Past papers: 2021 Fourth Summative SAQ.pdf (p2, Q1) [13] Senior notes: Ryan Ho Fundamentals.pdf (p191) [14] Senior notes: Adrian Lui Pediatrics Notes.pdf (p20) [15] Lecture slides: Block C - O&G Theme Case 1.docx.pdf (p7)
CFB PAE01 Paediatric History Taking
Paediatric history taking is the systematic process of gathering a child's clinical information—including presenting complaint, history of present illness, birth history, developmental milestones, immunisation status, feeding/nutrition, and family/social history—from the parent or caregiver to guide diagnosis and management.
CFB OGPAE01-2 Perinatal Medicine, Antenatal Care And Pre-pregnant Counselling (part II)
Continuation of perinatal medicine education covering advanced aspects of antenatal care, including screening strategies, management of high-risk pregnancies, and pre-pregnancy counselling to optimize maternal and fetal outcomes.