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Edward Syndrome (trisomy 18)

Edward syndrome is a severe chromosomal disorder caused by an extra copy of chromosome 18, typically presenting at birth with characteristic features including clenched fists with overlapping fingers, rocker-bottom feet, cardiac defects, and profound developmental disability, with most affected infants dying within the first year of life.

Exam domainOne-glance essentials
Definition / diagnosis
  • Severe multisystem chromosome disorder caused by trisomy 18 [1]
  • Most cases arise from meiotic nondisjunction [1]
Epidemiology / risks
  • Advanced maternal age increases risk [1]
  • Mosaic or partial trisomy can produce variable severity [1]
Core mechanism
  • Extra chromosome 18 disrupts fetal growth and organ development [1]
  • Marked prenatal-onset growth restriction is typical [1]
Clinical picture
  • Clenched fists with overlapping fingers, rocker-bottom feet and micrognathia [1]
  • Cardiac, renal and CNS malformations are common [1]
Investigations
  • Antenatal ultrasound and screening raise suspicion [2]
  • Karyotype or chromosomal microarray confirms the diagnosis [2]
Management
  • Provide individualised neonatal support and shared decision-making [3]
  • Treat feeding, respiratory and cardiac problems according to goals of care [3]
Complications
  • High fetal and infant mortality with profound developmental disability [4]
  • Apnoea, aspiration, infection and heart failure are frequent [4]
Prevention / follow-up
  • Genetic counselling clarifies usually low recurrence after nondisjunction [3]
  • Offer prenatal diagnosis in future pregnancies when desired [3]
Exam traps
  • Do not diagnose from phenotype alone [2]
  • Survival is variable; avoid presenting population outcomes as an individual certainty [3]

References

[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pp. 505–506)

[2] Senior notes: Adrian Lui Pediatrics Notes.pdf (pp. 505–506)

[3] Senior notes: Adrian Lui Pediatrics Notes.pdf (pp. 505–506)

[4] Senior notes: Adrian Lui Pediatrics Notes.pdf (pp. 505–506)

Edward Syndrome (Trisomy 18) — Paediatric Clinical Notes

Edward syndrome is a chromosomal disorder caused by the presence of an extra copy (whole or partial) of chromosome 18 [1][2]. The name comes from John H. Edwards, who first described the syndrome in 1960.

  • "Trisomy" → Greek: "tri" = three, "soma" = body → three copies of a chromosome instead of the normal two.
  • Chromosome 18 is one of the smaller autosomes, but it carries ~300 genes, many critical for embryonic development, cardiac morphogenesis, and neurological formation.
  • It is classified as a lethal chromosomal abnormality — the majority of prenatally diagnosed cases die in utero, and among live births, 50% die within the first 2 weeks of life; only 5–10% survive the first year [2].

Key Concept

Edward syndrome is the second most common autosomal trisomy observed in live births (after Down syndrome / Trisomy 21). Despite being "common" among trisomies, it is almost universally fatal — this distinguishes its prognostic counselling dramatically from Trisomy 21.

2. Epidemiology

  • Incidence: approximately 1 in 3,000 live births [1], though some sources cite 1 in 5,000–8,000 due to differing inclusion of stillbirths. Felix Lai's notes quote 1 in 15,000 births [2] — this lower figure may reflect only confirmed live births surviving to postnatal assessment. The discrepancy arises because a substantial proportion are lost prenatally.
  • The conception incidence is much higher (~1 in 2,500 pregnancies) because most affected embryos are spontaneously aborted.
  • Incidence increases with advanced maternal age (same mechanism as Trisomy 21).

  • Female predominance: M:F ≈ 1:3 to 1:4 [1][2].
  • The reason for this is not fully understood [1], but proposed explanations include:
    • Preferential in utero loss of affected males — male fetuses with Trisomy 18 may have a higher spontaneous abortion rate.
    • Possible protective effect of a second X chromosome in females (speculative).

TimepointSurvival
Prenatal detection → live birth~50% die in utero
First 2 weeks of life~50% of live births die
First yearOnly 5–10% survive [2]
Median survival (live births)~14 days [1]
  • Extended survival is possible [1], particularly in mosaic Trisomy 18 or with aggressive supportive care, but the vast majority have profound disability.

High Yield — Exam Point

Second most common autosomal trisomy in live births (after T21). Female predominance (M:F = 1:3–4). Median survival = 14 days. Only 5% reach 1 year [1][2].

3. Risk Factors

  • The primary risk factor is advanced maternal age, just as with Trisomy 21 [2].
  • Why? During oogenesis, primary oocytes are arrested in prophase I of meiosis from fetal life. Over decades, the prolonged meiotic arrest leads to:
    • Degradation of cohesin proteins holding sister chromatids together.
    • Loss of chiasma maintenance.
    • Increased risk of non-disjunction — failure of paired chromosomes (or sister chromatids) to separate properly during meiosis I or II.
  • The extra chromosome 18 typically arises from maternal meiosis I non-disjunction (~60%) or maternal meiosis II non-disjunction (~30%).

  • Low recurrence risk for full Trisomy 18 (typically quoted as ~1% above age-related baseline) [1].
  • Exception: Robertsonian translocation or balanced translocation carriers have a significantly higher recurrence risk [1] — parental karyotyping is therefore essential after any trisomy diagnosis.

  • If a parent carries a balanced translocation involving chromosome 18, the recurrence risk depends on the specific translocation and which parent carries it.

Understanding why an extra chromosome 18 causes such devastating effects requires understanding what genes reside on it:

RegionKey Genes / LociRelevance
18qTGIF (TG-interacting factor)Involved in holoprosencephaly pathway
18qBCL2Anti-apoptotic oncogene — overexpression disrupts normal programmed cell death during organogenesis
18qMC4RMelanocortin receptor — involved in growth regulation
18pVarious developmental genesBrain and craniofacial development
  • The gene dosage imbalance (3 copies instead of 2 → ~150% normal gene product) disrupts tightly regulated developmental pathways. This is why trisomies of larger chromosomes (with more genes) are almost always lethal, while trisomies of smaller chromosomes (13, 18, 21) or sex chromosomes are the only ones compatible with live birth.

Why Are Only Trisomies 13, 18, 21 (and Sex Chromosomes) Seen in Live Births?

Chromosomes 13, 18, and 21 are relatively gene-poor compared to other autosomes. The gene dosage imbalance from having 3 copies is therefore "less catastrophic" — though still usually lethal for T13 and T18. Trisomy of gene-rich chromosomes (e.g., chromosome 1) causes such severe developmental disruption that the embryo fails very early and is spontaneously aborted before clinical recognition.

5. Aetiology and Pathophysiology

5.1 Genetic Mechanisms

Three genetic mechanisms produce Edward syndrome [2]:

  • 90% are caused by meiotic non-disjunction [2].
  • Non-disjunction: during meiosis (usually maternal meiosis I), the two copies of chromosome 18 fail to separate. One gamete receives 2 copies, the other receives 0. Fertilisation of the gamete with 2 copies by a normal sperm → zygote with 3 copies (trisomy).
  • Associated with advanced maternal age [2].
  • All cells in the body carry 47 chromosomes → most severe phenotype.

  • Presence of 3 copies of chromosome 18 in some cells and 2 copies in others [2].
  • Caused by mitotic non-disjunction or translocation error after fertilisation [2] — i.e., the initial zygote is normal (46 chromosomes), but during early mitotic divisions, one cell line loses or gains a chromosome 18.
  • Phenotype is extremely variable, ranging from apparently normal to similar to complete trisomy [2].
  • The severity depends on:
    • Proportion of trisomic cells.
    • Distribution — which tissues/organs contain the trisomic cells.
    • Timing of the mitotic error — earlier errors → more cells affected → more severe.

  • Partial trisomy 18 may result from a balanced translocation or inversion carried by 1 parent [2].
  • Only a segment of chromosome 18 is present in triplicate — phenotype depends on which genes are duplicated.
  • Critical region: the long arm of chromosome 18 (18q11→18q12) is thought to contain the "critical region" responsible for the classic phenotype.
  • Important: if a parent carries a balanced translocation, recurrence risk is significantly higher than sporadic full trisomy → parental karyotyping is essential.

The extra chromosome 18 causes gene dosage imbalance → overexpression of chromosome 18 genes → disruption of:

  1. Cardiac morphogenesis → congenital heart defects (virtually 100%)
  2. CNS development → microcephaly, cerebellar hypoplasia, intellectual disability
  3. Musculoskeletal patterning → clenched fists, rocker-bottom feet, short sternum
  4. Renal development → horseshoe kidney, hydronephrosis
  5. Craniofacial development → micrognathia, low-set ears, prominent occiput
  6. Growth → severe intrauterine growth restriction (IUGR)

The BCL2 gene on 18q21 (anti-apoptosis) is overexpressed → dysregulated apoptosis during organogenesis → aberrant structural development.

TypeKaryotypeProportionMechanismPhenotype Severity
Full Trisomy 1847, XX+18 or 47, XY+18~94%Meiotic non-disjunctionSevere (classic)
Mosaic Trisomy 1847, +18 / 46~5%Post-zygotic mitotic errorVariable (mild → severe)
Partial Trisomy 18Various translocations~1%Parental balanced translocation/inversionDepends on duplicated segment

Exam Pearl

When you encounter a child with features "suggestive" of Trisomy 18 but milder presentation or longer survival than expected, think mosaic Trisomy 18. The phenotype can range from apparently normal to full-blown Edward syndrome.

7. Clinical Features

The clinical features of Edward syndrome are extensive and affect virtually every organ system. The hallmark is a combination of IUGR + characteristic hand posture (clenched fists with overlapping fingers) + cardiac malformations + distinctive craniofacial features.

SymptomPathophysiological Basis
Low birth weight (> 90% of cases) [1]Severe IUGR due to placental insufficiency + impaired fetal growth from gene dosage imbalance affecting growth factors
Poor feeding / feeding difficultiesMicrognathia (small jaw) → difficulty latching; CNS impairment → poor suck-swallow coordination; oesophageal atresia (in some)
Weak cryCNS involvement — cerebellar hypoplasia, generalised hypotonia progressing to hypertonia
Failure to thriveCombination of cardiac failure (high-output demands from CHD), feeding difficulties, and intrinsic growth impairment
Respiratory distressCongenital heart disease (pulmonary overcirculation from VSD), diaphragmatic eventration, or central apnoea from CNS malformation
SeizuresStructural brain abnormalities → abnormal cortical excitability
Apnoeic episodesCentral apnoea from brainstem/cerebellar malformation

7.2 Signs (What You Find on Examination)

SignPathophysiological Basis
Microcephaly [1]Impaired brain growth — gene dosage imbalance disrupts neuronal proliferation and migration
Prominent occiput (dolichocephaly) [1]Abnormal calvarial bone growth — elongated skull shape due to disproportionate cranial bone development (premature closure or abnormal growth of certain sutures)
Short neck [1]Defective cervical vertebral and soft tissue development
Dysplastic / malformed ears [1]Abnormal first and second branchial arch development → low-set, posteriorly rotated, with pointed helices ("fawn-like" ears)
Small mouth and chin (micrognathia) [1]Mandibular hypoplasia from first branchial arch developmental defect
Narrow palpebral fissuresPeriorbital tissue underdevelopment
Epicanthic foldsMidface hypoplasia

Distinguishing the Occiput

In Trisomy 18: the occiput is prominent (the back of the head "sticks out"). In Trisomy 21: the occiput is flat (brachycephaly). This is a classic differentiating exam point.

SignPathophysiological Basis
Flexed, overlapping fingers / clenched hands (95%) [1]Characteristic hand posture: 2nd finger overlaps 3rd, 5th overlaps 4th — due to abnormal muscle tone and joint/tendon development from chromosome 18 gene dosage effects on connective tissue and neuromuscular patterning
Rocker-bottom feet with prominent heels (90%) [1]Abnormal tarsal bone development → convex sole with prominent calcaneus; "rocker-bottom" = the foot looks like the bottom of a rocking chair
Short, prominent sternum and widely spaced nipples [1]Short sternum (due to abnormal sternal ossification centre development) → shield-like chest configuration
Hypoplastic nailsDistal limb growth impairment
Limited hip abductionAbnormal acetabular development
Radial aplasia / hypoplasia (occasionally)Limb bud patterning defect
Classic Hand Posture in Trisomy 18:

    Index finger (2nd) overlaps middle finger (3rd)
    Little finger (5th) overlaps ring finger (4th)
    Fists are tightly clenched

    This is virtually PATHOGNOMONIC and present in ~95% of cases.

High Yield — The Clenched Fist

The clenched fist with overlapping fingers is the single most recognisable and frequently tested physical sign of Trisomy 18. Remember the pattern: 2nd over 3rd, 5th over 4th. In contrast, a single transverse palmar crease is associated with Trisomy 21 and Trisomy 13.

Cardiac defects are present in virtually 100% of cases [1].

Cardiac DefectFrequencyPathophysiological Basis
Ventricular Septal Defect (VSD)Most common (94%) [1]Failure of interventricular septum to close during cardiac morphogenesis (weeks 4–8); gene dosage imbalance disrupts endocardial cushion development
Myxomatous change of valvesCommon [1]Abnormal extracellular matrix deposition in valve leaflets → thickened, redundant, incompetent valves (polyvalvular disease)
Atrial Septal Defect (ASD)CommonIncomplete atrial septum formation
Patent Ductus Arteriosus (PDA)CommonFailure of DA closure mechanisms
Coarctation of Aorta (CoA)Less commonAbnormal aortic arch development
Double-outlet right ventricleOccasionalConal septal malalignment

Why is cardiac involvement so severe and universal? Chromosome 18 genes are critically involved in cardiac neural crest cell migration and endocardial cushion formation. The 150% gene dosage disrupts the precise temporal and spatial signalling required for cardiac septation → almost all patients have structural heart disease.

Polyvalvular disease (myxomatous change of valves) is relatively specific to Trisomy 18 — it is less commonly seen in other trisomies and can be a clue on fetal echocardiography.

FeaturePathophysiological Basis
Cerebellar hypoplasia (most common, 32%) [1]Chromosome 18 genes involved in cerebellar granule cell proliferation → insufficient development
Severe intellectual disabilityGlobal cortical developmental impairment
Hypotonia (initially) → hypertoniaEvolving tone abnormalities due to upper motor neuron pathway dysfunction
SeizuresAbnormal cortical architecture → epileptogenicity
ApnoeaCentral apnoea from brainstem immaturity/malformation

FeaturePathophysiological Basis
Renal anomalies [1]Horseshoe kidney, hydronephrosis, ectopic kidney, renal agenesis — due to disrupted metanephric development

FeatureNotes
Single umbilical arteryNormally 2 arteries + 1 vein; SUA associated with multiple congenital anomalies
Omphalocele / diaphragmatic herniaMidline closure defects from abnormal body wall development
Cryptorchidism (in males)Impaired testicular descent
Cleft lip/palate (occasional)Midface developmental disruption

  • Oesophageal atresia (OA) — Trisomy 18 is one of the chromosomal disorders associated with the VACTERL association and oesophageal atresia [3]. This is clinically important because:
    • If a neonate presents with OA, chromosomal analysis should be performed.
    • The presence of T18 significantly worsens the prognosis of OA repair.

VACTERL Association and Trisomy 18

While VACTERL association and Trisomy 18 can both feature oesophageal atresia/tracheo-oesophageal fistula, cardiac anomalies, and renal/vertebral anomalies, they are distinct entities. However, 50–70% of oesophageal atresia cases are associated with VACTERL, T13/T18/T21, or CHARGE syndrome [3]. Always check karyotype in a neonate with OA.

SystemKey FeaturesFrequency
GrowthLow birth weight, IUGR> 90%
CraniofacialMicrocephaly, prominent occiput, dysplastic ears, micrognathia> 90%
HandsClenched fists with overlapping fingers95%
FeetRocker-bottom feet90%
ChestShort sternum, widely spaced nipplesCommon
CardiacVSD (94%), polyvalvular disease~100%
NeurologicalCerebellar hypoplasia, intellectual disability, seizures> 80%
RenalHorseshoe kidney, hydronephrosis~60%
GIOA/TOF, omphalocele, malrotation~15–30%
GUCryptorchidismCommon in males

8. Growth and Development Considerations

  • Almost all infants with Trisomy 18 demonstrate severe IUGR with birth weight often < 2,500g even at term.
  • Postnatal growth is severely impaired — specific Trisomy 18 growth charts exist but are rarely used given the poor prognosis.

  • Profound global developmental delay in all survivors.
  • Milestones are severely delayed or never achieved.
  • Even in mosaic cases with milder phenotype, significant intellectual disability is expected.

9. Family-Centred Care and Communication

When Trisomy 18 is diagnosed prenatally (via NIPT, amniocentesis, or CVS):

  • Non-directive counselling — present factual information about prognosis, quality of life, and options.
  • Options include:
    • Continuation of pregnancy with comfort care at birth.
    • Continuation with limited intervention plan.
    • Termination of pregnancy (where legal and acceptable to the family).
  • In Hong Kong, termination is legally available up to 24 weeks' gestation for severe fetal abnormality.

  • Goals of care discussions are essential — the family must be involved in decisions about:
    • Resuscitation at birth.
    • Level of intervention (e.g., cardiac surgery, ventilation).
    • Comfort/palliative care.
  • There is increasing recognition that some families choose intervention — centres in Japan and some Western centres report improved survival with cardiac surgery and full intervention, though quality of life remains a concern.
  • All decisions are made by parents/legal guardians in the neonatal period.
  • The paediatric team should involve clinical ethics and palliative care teams when there is disagreement about goals of care.

  • Most die prenatally or in infancy [1].
  • Median survival: 14 days [1].
  • Only 5% reach 1 year [1].
  • Extended survival is possible [1], particularly with:
    • Mosaic Trisomy 18.
    • Full intervention including cardiac surgery.
    • Children surviving past 1 year can occasionally survive into teens/adulthood with profound disability.
  • Low recurrence risk (for full trisomy cases) [1], except in Robertsonian translocation or balanced translocation carriers [1].

  • In Hong Kong, the universal antenatal screening programme includes:
    • First-trimester combined screening (maternal age + nuchal translucency + serum markers) — can detect T18.
    • Non-invasive prenatal testing (NIPT) using cell-free fetal DNA — increasingly used as first-line or second-tier screening; very high sensitivity and specificity for T18 (> 95% detection rate, very low false positive rate).
    • Confirmatory testing by amniocentesis or chorionic villus sampling (CVS) with karyotype or chromosomal microarray.
  • The Hospital Authority provides genetic counselling services through the Clinical Genetics Service at Queen Mary Hospital and other tertiary centres.
  • Given the small but significant proportion caused by parental translocation, parental karyotyping should be offered after any confirmed case of Trisomy 18.

High Yield Summary

Edward Syndrome (Trisomy 18) — Pre-DDx/Dx/Mx Summary

  1. Definition: Extra chromosome 18 → lethal chromosomal abnormality
  2. Epidemiology: 2nd most common autosomal trisomy; 1/3,000–1/15,000 live births; F > M (4:1); increases with maternal age
  3. Genetics: ~94% full trisomy (meiotic non-disjunction), ~5% mosaic (mitotic error), ~1% translocation (familial risk)
  4. Cardinal clinical features:
    • Microcephaly with prominent occiput
    • Clenched fists with overlapping fingers (2nd over 3rd, 5th over 4th) — 95%
    • Rocker-bottom feet — 90%
    • Cardiac defects in ~100%, most commonly VSD (94%) and polyvalvular myxomatous disease
    • Low birth weight (> 90%)
    • Cerebellar hypoplasia (most common CNS anomaly)
  5. Prognosis: Median survival = 14 days; only 5% survive to 1 year
  6. Recurrence: Low, unless parental balanced translocation → always offer parental karyotyping
  7. Distinguish from T21: Prominent occiput (T18) vs flat occiput (T21); clenched fists (T18) vs single palmar crease (T21)
  8. Distinguish from T13: T13 classical triad = microphthalmos + cleft lip/palate + polydactyly

Active Recall — Edward Syndrome (Trisomy 18): Definition to Clinical Features

[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pp. 505–506) [2] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 838) [3] Senior notes: Maksim Surgery Notes.pdf (p. 331) — Oesophageal atresia and VACTERL/T18 association [4] Lecture slides: Block C - The malformed child: hereditary syndromes and anomalies.pdf [5] Lecture slides: GC 151. The malformed child hereditary syndromes and anomalies.pdf [6] Senior notes: Ryan Ho Opthalmology.pdf (p. 122) — Congenital cataract associations including Edward syndrome

Differential Diagnosis of Edward Syndrome (Trisomy 18)

Edward syndrome presents with a constellation of features — IUGR, craniofacial dysmorphism, limb anomalies, and cardiac defects — that overlap with several other chromosomal, syndromic, and non-chromosomal conditions. In clinical practice, the differential arises in two main scenarios:

  1. Antenatally: Ultrasound findings (IUGR, cardiac defect, clenched fists, choroid plexus cysts) raise suspicion — the DDx is other causes of multiple congenital anomalies detected on screening.
  2. Postnatally: A dysmorphic neonate with multiple anomalies — the DDx is other genetic syndromes that share overlapping features before karyotype results return.

The key principle: No single feature is pathognomonic in isolation. It is the pattern recognition — the specific combination of features — that narrows the diagnosis. Confirmation always requires cytogenetic analysis (karyotype, FISH, or chromosomal microarray).

ConditionOverlapping Features with T18Distinguishing FeaturesCardiac Defect Pattern
Patau syndrome (Trisomy 13) [1]Microcephaly, dysplastic ears, low birth weight, cardiac defects, renal anomalies, lethal prognosisClassical triad: microphthalmos + cleft lip/palate + postaxial polydactyly; scalp defects; holoprosencephaly (HPE); single palmar creaseASD, TOF, TGA (NOT VSD predominant) [1]
Down syndrome (Trisomy 21) [1]Cardiac defects, low birth weight possible, hypotonia, dysplastic earsFlat occiput (vs prominent in T18); upslanting palpebral fissures; protruding tongue; single palmar crease; sandal gap; hypotonia (vs hypertonia in T18); much better prognosisAVSD (most characteristic), VSD [7]
Turner syndrome (45,X) [1]Short stature, widely spaced nipples, webbed neck, cardiac defects, renal anomaliesOnly females; lymphoedema at birth (not clenched fists); cubitus valgus; short 4th metacarpal; ovarian dysgenesis; normal intelligenceLeft-sided lesions: CoA, bicuspid AV [1][8]
Noonan syndrome [8]Short stature, widely spaced nipples, webbed neck, cardiac defects, low-set ears, dysmorphic faciesAutosomal dominant (RAS-MAPK pathway); downslanting palpebral fissures; ptosis; cryptorchidism; normal karyotype; hypertelorismRight-sided lesions: pulmonary valve stenosis, HCM [8]
DiGeorge syndrome (22q11.2 deletion) [8][9]Cardiac defects, micrognathia, low-set ears, feeding difficultiesCATCH-22 mnemonic: Cardiac (conotruncal), Abnormal facies, Thymic hypoplasia, Cleft palate, Hypocalcaemia; no clenched fists or rocker-bottom feetConotruncal: interrupted aortic arch, truncus arteriosus, TOF [8][9]
Smith-Lemli-Opitz syndromeIUGR, microcephaly, micrognathia, cardiac defects, renal anomalies, 2-3 toe syndactylyAutosomal recessive (7-dehydrocholesterol reductase deficiency); 2-3 toe syndactyly (pathognomonic); ambiguous genitalia in males; low cholesterol levels; no overlapping fingersVSD, ASD, AVSD
Pena-Shokeir syndrome (Fetal Akinesia Sequence)IUGR, clenched hands/camptodactyly, rocker-bottom feet, pulmonary hypoplasiaPolyhydramnios + fetal akinesia; multiple joint contractures (arthrogryposis); lung hypoplasia is the cause of death (not cardiac); no specific cardiac defect patternVariable
Distal arthrogryposis syndromesClenched fists, overlapping fingers, camptodactylyContractures but no cardiac defects, no IUGR, no craniofacial features; normal karyotype; familial (AD); preserved intellectNone typically
Fetal alcohol spectrum disorder (FASD)IUGR, microcephaly, cardiac defects (VSD), micrognathiaMaternal alcohol exposure history; smooth philtrum; thin vermillion border; short palpebral fissures; no clenched fists or rocker-bottom feetVSD, ASD
CHARGE syndromeCardiac defects, ear anomalies, IUGR, feeding difficultiesCHD7 gene mutation; Coloboma; Heart defects; Atresia choanae; Retardation of growth; Genital anomalies; Ear anomalies; cranial nerve dysfunctionTOF, AV canal, aortic arch anomalies

Systematic Approach to DDx by Presenting Feature

The clenched fist with overlapping fingers is highly suggestive of T18 but the DDx includes:

  • Pena-Shokeir syndrome (fetal akinesia) — arthrogryposis is generalised, hands are in a "frog-like" posture, lung hypoplasia dominates
  • Distal arthrogryposis — isolated hand/foot contractures, no systemic features
  • Restrictive dermopathy — tight shiny skin, arthrogryposis, lethal
  • Trisomy 18 — confirmed by the combination with prominent occiput + VSD + rocker-bottom feet

DifferentialKey distinguishing antenatal USS finding
Trisomy 18Clenched fists, single umbilical artery, choroid plexus cysts, strawberry-shaped skull, polyhydramnios
Trisomy 13Holoprosencephaly, polydactyly, midline facial clefting
Trisomy 21Nuchal thickening, absent/hypoplastic nasal bone, echogenic bowel, duodenal atresia ("double bubble")
Turner syndromeCystic hygroma, hydrops fetalis, coarctation
Triploidy (69,XXX/XXY)Very severe asymmetric IUGR, large cystic placenta (partial mole)

VSD is the most common congenital heart defect overall and is seen in many syndromes. The associated dysmorphic features guide the DDx:

VSD + ...Think of...
VSD + prominent occiput + clenched fists + rocker-bottom feetTrisomy 18
VSD + flat occiput + upslanting eyes + single palmar creaseTrisomy 21
VSD + polydactyly + cleft lip + microphthalmosTrisomy 13
VSD + elfin facies + hypercalcaemiaWilliams syndrome (though supravalvular AS more characteristic)
VSD + absent thymus + hypocalcaemiaDiGeorge syndrome

Trisomy 18 vs Trisomy 13 vs Trisomy 21 — Exam Classic

FeatureTrisomy 18 (Edward)Trisomy 13 (Patau)Trisomy 21 (Down)
OcciputProminentSloping foreheadFlat (brachycephaly)
HandsClenched, overlapping fingersSingle palmar crease, polydactylySingle palmar crease, clinodactyly
FeetRocker-bottomRocker-bottom possibleSandal gap
EyesNarrow palpebral fissuresMicrophthalmos, colobomaUpslanting, Brushfield spots
MouthMicrognathiaCleft lip ± palateProtruding tongue
ScalpNormalScalp defects (aplasia cutis)Normal
BrainCerebellar hypoplasiaHoloprosencephalyGenerally normal structure
CardiacVSD (94%), polyvalvular diseaseASD, TOF, TGAAVSD (most characteristic), VSD
Most common CHDVSD [1]ASD [1]AVSD [7]
SurvivalMedian 14 daysSimilar to T18Median ~60 years
F:M ratio4:1 (F > M)Equal1:1

Common Exam Trap

Students often confuse the cardiac defect patterns between the three autosomal trisomies. Remember:

  • T18 → VSD (94%) + polyvalvular disease
  • T13 → ASD, TOF, TGA
  • T21 → AVSD (most characteristic / "classic") + VSD

Also, rocker-bottom feet can occur in both T18 and T13, but the clenched fist with overlapping fingers is highly specific to T18 [1][7].

Conditions Associated with Overlapping Features — Expanded Discussion

  • Incidence: 1/8,000 live births [1].
  • Why it overlaps: same category (autosomal trisomy), same mechanism (non-disjunction), similarly lethal.
  • Classical triad: microphthalmos + cleft lip/palate + polydactyly (postaxial) [1].
  • Key differentiators: scalp defects (aplasia cutis congenita), holoprosencephaly (midline brain fusion failure — can range from alobar HPE to mild form), microphthalmia/cyclopia in severe cases [1][7].
  • Prognosis: same as Edward syndrome [1] — median survival ~7–10 days, < 10% survive 1 year.

  • Most common autosomal trisomy and most common genetic cause of intellectual disability [1].
  • Incidence: ~1/600–800 live births [1].
  • Key differentiators from T18:
    • Hypotonia (T21) vs hypertonia (T18)
    • Flat occiput / brachycephaly (T21) vs prominent occiput (T18)
    • Good prognosis (T21, life expectancy ~60y) vs lethal (T18)
    • GI associations in T21: duodenal atresia, Hirschsprung disease [7]

  • Only females affected (monosomy X).
  • Overlaps with T18 in: widely spaced nipples, short neck, cardiac defects, renal anomalies.
  • Key differentiators: lymphoedema at birth (puffy hands/feet — not clenched), cystic hygroma on antenatal scan, short stature (SHOX gene haploinsufficiency), ovarian dysgenesis, normal to near-normal intelligence [1].
  • Cardiac lesions are left-sided: bicuspid aortic valve, coarctation [1][8].

  • Autosomal dominant (RAS-MAPK pathway mutations — PTPN11 most common).
  • Phenotypically resembles Turner but normal karyotype, affects both sexes.
  • Key differentiators: downslanting (not upslanting) palpebral fissures, ptosis, pulmonary stenosis with dysplastic valve (right-sided lesions) [8], bleeding diathesis.
  • No clenched fists or rocker-bottom feet.

  • Microdeletion on chromosome 22 — most common microdeletion syndrome.
  • Mnemonic: CATCH-22 — Cardiac, Abnormal facies, Thymic hypoplasia, Cleft palate, Hypocalcaemia; chromosome 22 [9].
  • Cardiac defects are conotruncal: interrupted aortic arch (type B), truncus arteriosus, TOF [8][9].
  • Key differentiators from T18: presence of hypocalcaemia (hypoparathyroidism), immunodeficiency (T-cell deficit from thymic hypoplasia), no limb anomalies typical of T18.

  • When an omphalocele is detected (a feature that can occur in T18), the DDx includes:
    • Trisomy 18 — omphalocele + cardiac defect + clenched fists + IUGR
    • Beckwith-Wiedemann syndrome — omphalocele + macrosomia (opposite of IUGR!) + macroglossia + ear creases; associated with hepatoblastoma [10]
    • Isolated omphalocele — no syndromic features
  • The distinction is critical because omphalocele in T18 has a much worse prognosis than in Beckwith-Wiedemann or isolated cases [10].

  • Edward syndrome (Trisomy 18) is listed as an associated syndrome for hepatoblastoma [10], along with Beckwith-Wiedemann, FAP, Down syndrome, and Li-Fraumeni.
  • This is a rare but testable association.

Once clinical suspicion arises, the DDx is resolved by cytogenetic/molecular testing:

TestWhat It DetectsTurnaround
Rapid FISHAneuploidy for chromosomes 13, 18, 21, X, Y24–48 hours
KaryotypeFull chromosomal complement; translocations, mosaicism7–14 days
Chromosomal Microarray (CMA)Copy number variants including microdeletions (e.g., 22q11.2)2–4 weeks
NIPT (antenatal)Cell-free fetal DNA screening for T13/T18/T215–10 days

When to Suspect Trisomy 18 Over Other DDx

The combination of prominent occiput + clenched fists with overlapping fingers (2nd over 3rd, 5th over 4th) + rocker-bottom feet + VSD is virtually diagnostic pending karyotype confirmation. No other common condition produces this exact constellation.

Active Recall — Differential Diagnosis of Trisomy 18

References

[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pp. 503–506) [7] Senior notes: Maksim Paediatric Notes.pdf (p. 204) [8] Senior notes: Ryan Ho Cardiology.pdf (p. 185) — Syndromes associated with congenital heart diseases [9] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 581) — DiGeorge syndrome / CATCH-22 [10] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (p. 1077) — Hepatoblastoma associations including T18; Maksim Surgery Notes.pdf (p. 333) — Omphalocele associations

Diagnostic Criteria, Algorithm, and Investigations for Edward Syndrome (Trisomy 18)

1. Diagnostic Criteria

There are no formal "diagnostic criteria" for Trisomy 18 in the way that, say, rheumatic fever has the Jones criteria. The diagnosis is ultimately cytogenetic — you need to demonstrate the extra chromosome 18 in the laboratory. However, the clinical pathway has two phases: clinical suspicion (pattern recognition) and cytogenetic confirmation.

Clinical suspicion is raised when a neonate (or fetus on antenatal scan) demonstrates the characteristic pattern of anomalies:

Postnatal clinical suspicion — presence of ≥3 of the following in combination should trigger urgent karyotype:

Cardinal FeatureApproximate Frequency
Low birth weight / IUGR> 90% [1]
Microcephaly with prominent occiput> 90% [1]
Clenched fists with overlapping fingers (2nd over 3rd, 5th over 4th)95% [1]
Rocker-bottom feet with prominent heels90% [1]
Congenital heart defect (especially VSD ± polyvalvular disease)~100% [1]
Dysplastic/malformed ears> 80% [1]
Micrognathia (small mouth and chin)> 80% [1]
Short sternum with widely spaced nipplesCommon [1]

Antenatal suspicion — ultrasound findings that should prompt further investigation:

Antenatal USS FindingNotes
IUGR (especially early and symmetrical)Non-specific but raises suspicion in combination
Choroid plexus cystsPresent in ~1% of normal fetuses — only significant when combined with other markers
Clenched fists / overlapping fingersHighly suggestive when persistent
Single umbilical arteryAssociated with chromosomal abnormalities
Cardiac defect (especially VSD)Prompts fetal karyotyping
Strawberry-shaped skull (prominent occiput)Characteristic cranial shape
Rocker-bottom feetHighly suggestive
OmphaloceleConsider T18 in DDx of omphalocele
PolyhydramniosDue to impaired fetal swallowing

Key Principle — Clinical vs Cytogenetic Diagnosis

Clinical features raise suspicion; cytogenetic analysis confirms the diagnosis. You cannot diagnose Trisomy 18 on clinical features alone — there is always overlap with other syndromes. The definitive diagnosis requires demonstration of an extra chromosome 18 (or its material) by karyotype, FISH, or chromosomal microarray (CMA) [2].

The diagnosis is confirmed when one of the following is demonstrated:

Karyotype FindingTypeClinical Correlation
47, XX+18 or 47, XY+18Full Trisomy 18Classic phenotype; ~94% of cases; caused by meiotic non-disjunction [2]
47, +18 / 46 (mixed cell lines)Mosaic Trisomy 18Variable phenotype; ~5%; caused by post-zygotic mitotic error [2]
Partial duplication of 18q material via translocationPartial Trisomy 18Phenotype depends on segment; ~1%; may result from balanced translocation carried by parent [2]

2. Diagnostic Algorithm

The algorithm depends on whether the diagnosis is being pursued antenatally or postnatally.

The antenatal detection pathway in Hong Kong follows the standard screening cascade:

  1. First-trimester combined screening (11–13+6 weeks):

    • Maternal age
    • Nuchal translucency (NT) measurement — increased NT in T18
    • Maternal serum markers: PAPP-A (low) + free β-hCG (low)
    • In T18, both PAPP-A and free β-hCG are low — this is distinct from T21 where β-hCG is high

  2. Non-invasive prenatal testing (NIPT) — cell-free fetal DNA from maternal blood:

    • Increasingly used as first-line or second-tier screening in Hong Kong
    • Detection rate for T18 > 95%, with very low false positive rate (~0.1%)
    • NIPT is a screening test, NOT diagnostic — positive results require confirmatory invasive testing

  3. Invasive confirmatory testing (offered when screening is positive):

    • Chorionic villus sampling (CVS) — performed at 11–14 weeks; provides placental cells for karyotype/CMA
    • Amniocentesis — performed at ≥15 weeks; provides fetal cells from amniotic fluid
    • Both carry ~0.1–0.5% miscarriage risk

  4. Second-trimester anomaly scan (18–22 weeks):

    • May detect structural anomalies (cardiac defects, clenched fists, rocker-bottom feet, choroid plexus cysts) even if first-trimester screening was normal or declined

NIPT Serum Markers — T18 vs T21

In Trisomy 18: both PAPP-A and free β-hCG are LOW ("everything is low — the baby is failing"). In Trisomy 21: PAPP-A is LOW but free β-hCG is HIGH. This distinction is frequently tested. The mnemonic: T18 = "All Down" (both markers down); T21 = "One Up, One Down" (β-hCG up, PAPP-A down).

When a neonate is born with features suggestive of Trisomy 18:

  1. Clinical assessment — full dysmorphology examination by the paediatric team
  2. Urgent FISH — sent from peripheral blood for rapid result (24–48 hours)
  3. Full karyotype — from peripheral blood lymphocytes (7–14 days turnaround)
  4. Chromosomal microarray (CMA) — if karyotype is normal but clinical suspicion persists (detects submicroscopic duplications/deletions)
  5. Concurrent investigations to delineate associated anomalies:
    • Echocardiography (cardiac defects)
    • Renal ultrasound (renal anomalies)
    • Cranial ultrasound (cerebellar hypoplasia, other CNS malformations)
    • Ophthalmological assessment

3. Investigation Modalities — Key Findings and Interpretations

InvestigationSpecimenKey Finding in T18TurnaroundInterpretation Notes
Rapid FISHPeripheral blood / amniotic fluid / CVS3 signals for chromosome 18 probe (normally 2)24–48 hoursRapid preliminary confirmation; does NOT detect translocations or mosaicism reliably
G-banded karyotypePeripheral blood lymphocytes / amniotic fluid / CVS47, XX+18 or 47, XY+18 (full trisomy); or 47, +18 / 46 (mosaic); or structural rearrangement (translocation)7–14 daysGold standard for full chromosomal analysis; identifies type (full vs mosaic vs translocation); counts 20+ metaphases to assess mosaicism
Chromosomal microarray (CMA)Blood / tissueCopy number gain of entire chromosome 18 or partial segment2–4 weeksDetects submicroscopic gains/losses not visible on karyotype; particularly useful for partial trisomy or when karyotype is unexpectedly normal; cannot detect balanced translocations
NIPT (antenatal)Maternal bloodIncreased representation of chromosome 18 sequences in cell-free DNA5–10 daysScreening test only — sensitivity > 95%, specificity > 99.5%, but positive predictive value depends on prior probability (maternal age, prevalence); must be confirmed by invasive testing
Parental karyotypingParental bloodBalanced translocation involving chromosome 18 in one parent7–14 daysEssential when translocation Trisomy 18 is identified — determines recurrence risk for future pregnancies; if parental karyotypes are normal, translocation arose de novo (low recurrence risk) [2]

Why Is FISH Not Enough?

FISH gives a rapid answer (24–48h) by counting fluorescent signals for chromosome 18, but it cannot distinguish full trisomy from translocation, and it may miss low-level mosaicism. A full G-banded karyotype examining ≥20 metaphases is required to:

  1. Confirm the type (full vs mosaic vs translocation).
  2. Guide recurrence risk counselling.
  3. Determine if parental karyotyping is needed. Always send both FISH (for speed) AND karyotype (for completeness).

MarkerNormal FunctionFinding in T18Compare with T21
PAPP-A (Pregnancy-Associated Plasma Protein A)Protease that releases IGF from binding proteins → promotes placental/fetal growthLow — impaired placental functionLow
Free β-hCGSubunit of hCG maintaining corpus luteum and placental functionLow — impaired trophoblast functionHigh
Nuchal translucency (NT)USS measurement of fluid at fetal neck (11–13+6 weeks)Increased — lymphatic drainage dysfunction, cardiac failureIncreased

Why are both markers low in T18? The trisomic placenta is severely dysfunctional in T18 — both trophoblast-derived hCG production and PAPP-A secretion are impaired, reflecting the global developmental failure. In T21, the placenta is relatively better preserved (β-hCG is actually overproduced due to immature trophoblast proliferation).

If performed (less common now with NIPT available):

MarkerFinding in T18
AFP (alpha-fetoprotein)Low
uE3 (unconjugated oestriol)Low
hCGLow
Inhibin ALow

In T18, all four markers tend to be low — again reflecting global placental dysfunction. This is sometimes called the "all-low" pattern.

TimingUSS FindingSignificance
First trimesterIncreased nuchal translucencyNon-specific marker of chromosomal abnormality; due to impaired lymphatic drainage or cardiac dysfunction
First trimesterAbnormal ductus venosus flowReflects early cardiac dysfunction
Second trimesterChoroid plexus cystsFound in ~1% of normal fetuses; in isolation, low predictive value; in combination with other markers, increases T18 suspicion
Second trimesterClenched fists / overlapping fingersHighly suggestive when persistent
Second trimesterStrawberry-shaped cranium (prominent occiput + narrow bifrontal diameter)Characteristic cranial shape of T18
Second trimesterCardiac defect (VSD)Present in virtually all T18 fetuses; may be first finding prompting karyotype
Second trimesterRocker-bottom feetConvex sole visible on sagittal foot view
Second trimesterSingle umbilical arteryNormal = 2 arteries + 1 vein; SUA associated with chromosomal abnormalities
Second trimesterOmphaloceleMidline abdominal wall defect with herniated viscera covered by membrane
Second trimesterIUGRSymmetrical early-onset growth restriction
Second trimesterPolyhydramniosImpaired fetal swallowing due to CNS dysfunction or oesophageal atresia
Second trimesterRenal anomalies (horseshoe kidney, hydronephrosis)Abnormal metanephric development

Choroid Plexus Cysts — A Common Exam Discussion Point

Isolated choroid plexus cysts (CPCs) on second-trimester USS are common and usually benign (~1% of normal pregnancies). They only become significant when combined with other markers of T18. Current guidance: isolated CPCs in a low-risk patient with normal anatomy and normal first-trimester screening do NOT require amniocentesis. However, CPCs + any additional structural anomaly or abnormal screening → offer invasive testing.

Once T18 is confirmed (or strongly suspected), the following investigations are performed to guide management decisions:

InvestigationWhat It AssessesExpected Findings in T18
EchocardiographyCardiac anatomy and functionVSD (94%) [1]; polyvalvular myxomatous disease; ASD; PDA; may have complex defects
Renal ultrasoundRenal anatomyHorseshoe kidney; hydronephrosis; renal agenesis; ectopic kidney
Cranial ultrasoundBrain structure (through open fontanelle)Cerebellar hypoplasia (32%) [1]; other structural brain anomalies; ventriculomegaly
Ophthalmological examinationEye anomaliesCongenital cataract (T18 is a recognised syndromal cause of congenital cataract [6]); corneal opacity; microphthalmos (less common than T13)
Skeletal survey (if indicated)Bony anomaliesShort sternum; radial aplasia; vertebral anomalies
Abdominal USSGI anomaliesOmphalocele; malrotation
Hearing assessmentSensorineural / conductive hearing lossMay have hearing impairment due to ear dysplasia

InvestigationPurpose
Parental karyotypingTo identify balanced translocation carrier status; essential when translocation Trisomy 18 is found [2]; determines recurrence risk
Genetic counselling referralExplanation of diagnosis, prognosis, recurrence risk, and reproductive options for future pregnancies

ScenarioInterpretationNext Step
NIPT positive for T18Screening test only — not diagnosticOffer CVS or amniocentesis for confirmatory karyotype
FISH shows 3 signals for chr 18Preliminary confirmation of trisomyAwait full karyotype for type classification
Karyotype: 47, XX+18Full Trisomy 18 confirmedGoals of care discussion; concurrent organ assessment; genetic counselling
Karyotype: 47, +18 / 46Mosaic Trisomy 18Prognosis more variable; extent of mosaicism guides counselling; may need tissue karyotype (e.g., skin fibroblasts)
Karyotype: 46 chromosomes but with translocation involving chr 18Partial Trisomy 18Parental karyotyping essential [2]; higher recurrence risk if parent is carrier
Karyotype normal but clinical features suggestiveConsider alternative diagnosisSend CMA; consider other DDx (Pena-Shokeir, distal arthrogryposis, etc.)

Tissue Karyotype in Suspected Mosaicism

If blood karyotype is normal but clinical suspicion remains high, mosaicism may be confined to certain tissues. A skin fibroblast karyotype can detect tissue-confined mosaicism that blood lymphocyte karyotype misses. This is particularly relevant in suspected mosaic Trisomy 18 with a milder phenotype.

High Yield Summary — Diagnosis of Trisomy 18

  1. Clinical suspicion: Pattern of prominent occiput + clenched fists (2nd over 3rd, 5th over 4th) + rocker-bottom feet + VSD + IUGR
  2. Antenatal screening: NIPT (> 95% detection rate); first-trimester combined screening (both PAPP-A and free β-hCG are LOW in T18)
  3. Antenatal confirmation: CVS (11–14 weeks) or amniocentesis (≥15 weeks) → karyotype/CMA
  4. Postnatal confirmation: Urgent FISH (24–48h) + full G-banded karyotype (7–14 days) from peripheral blood
  5. Concurrent organ assessment: Echocardiography (VSD ~94%), renal USS, cranial USS, ophthalmology
  6. Parental karyotyping: Essential when translocation type identified — determines recurrence risk
  7. Three types: Full trisomy (94%) vs mosaic (5%) vs translocation (1%) — karyotype distinguishes them

Active Recall — Diagnosis of Trisomy 18

References

[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pp. 505–506) [2] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 838) [6] Senior notes: Ryan Ho Opthalmology.pdf (p. 122) — Congenital cataract syndromal associations including Edward syndrome

Management of Edward Syndrome (Trisomy 18)

Before discussing specific interventions, it is essential to understand the fundamental management principle for Trisomy 18:

There is no cure for Trisomy 18 [7]. Management is supportive, focused on regular screening for potential comorbidities, specific treatment (drug, surgery, transplantation where appropriate), and genetic counselling [7].

The management of Trisomy 18 is unique in paediatrics because it sits at the intersection of medical ethics, family-centred care, and palliative medicine. The decisions made are profoundly influenced by:

  1. The lethal nature of the condition — median survival 14 days, only 5% survive to 1 year [1][2].
  2. The values and wishes of the family.
  3. The evolving (and somewhat controversial) debate about whether aggressive intervention prolongs meaningful life or prolongs suffering.

There are broadly two management paradigms that exist on a spectrum:

ApproachPhilosophyPractice
Comfort / palliative care (traditional)T18 is a lethal condition; aggressive intervention prolongs dying, not livingWarmth, feeding support, family bonding; no ventilation or cardiac surgery; focus on quality of life
Individualised intervention (emerging, e.g., Japan, some Western centres)Some children with T18 can survive with intervention; families should be offered choicesSelected cardiac surgery, ventilatory support, feeding procedures; careful case-by-case assessment

Exam Framing — What to Say

In an HKUMed exam, the safest and most defensible approach is: "Management should be individualised and family-centred. A multidisciplinary team discussion including neonatologists, geneticists, cardiologists, and palliative care specialists should establish goals of care with the family. Both comfort care and limited intervention are valid options depending on the clinical context and family values." This avoids being dogmatically "no intervention" (outdated) or uncritically "full intervention" (controversial).

The management pathway follows a structured timeline:

  1. Antenatal management (when diagnosed prenatally)
  2. Delivery room / immediate postnatal management
  3. Neonatal period management (first 28 days)
  4. Ongoing care (for survivors beyond neonatal period)
  5. Genetic counselling and family support (throughout)

3. Detailed Management by Phase

ComponentDetails
Genetic counsellingNon-directive counselling — explain the diagnosis (Trisomy 18), expected features, prognosis (median 14 days, 5% 1-year survival), and range of outcomes. Present options without prescribing a particular course [7]
Reproductive optionsTermination of pregnancy — available in Hong Kong up to 24 weeks for severe fetal abnormality (Offences Against the Person Ordinance, Cap. 212). Continuation of pregnancy — with either comfort care or individualised intervention plan
Birth planningIf continuing, develop a detailed birth plan: delivery mode, resuscitation preferences, presence of neonatal team, who will be present, skin-to-skin contact, baptism/religious rites if desired
Delivery modeVaginal delivery is generally preferred — caesarean section is typically not performed for fetal indication alone in confirmed T18 given the lethal prognosis. However, maternal indications for caesarean still apply
MonitoringSerial USS to monitor growth, amniotic fluid volume (polyhydramnios may develop), and fetal wellbeing

Caesarean Section in Trisomy 18

A common exam discussion point: Caesarean section purely for fetal benefit is generally NOT indicated in confirmed full Trisomy 18, because the lethal prognosis means the risks of surgery to the mother are not justified by meaningful improvement in fetal outcome. This is distinct from maternal indications for caesarean (e.g., obstructed labour, placenta praevia) which remain valid.

ComponentDetailsRationale
ThermoregulationDry, wrap, skin-to-skin contactNeonates with T18 are often IUGR/low birth weight → high surface-area-to-volume ratio → rapid heat loss
Airway managementGentle suctioning if needed; positioningMicrognathia may cause upper airway obstruction (similar principle to Pierre Robin sequence)
ResuscitationBased on pre-agreed birth plan — may range from full NLS algorithm to comfort care onlyThe resuscitation plan should be documented antenatally if diagnosis is known. If postnatal diagnosis, initial stabilisation is reasonable while assessment occurs
Family bondingFacilitate immediate skin-to-skin, family photographs, memory makingThis may be the only time the family has with their child — every moment is precious
Rapid confirmationSend urgent FISH from cord blood or peripheral bloodEven if antenatal diagnosis was made, postnatal confirmation is standard practice

3.3 Supportive Care — The Foundation (All Patients)

Regardless of whether comfort care or active intervention is chosen, the following supportive measures apply:

InterventionIndicationDetails
Oral feeding (breast or bottle)If suck-swallow coordination is adequateMany T18 infants have poor suck reflex due to CNS impairment and micrognathia; oral feeding should be attempted but may not be achievable
Nasogastric (NG) tube feedingIf oral feeding is inadequate but not pursuing long-term interventionAllows enteral nutrition while preserving comfort; minimally invasive
Gastrostomy tubeIf pursuing individualised intervention and long-term survival anticipatedPlaced surgically or endoscopically; allows long-term enteral feeding; indicated in survivors with persistent feeding difficulties

Why is feeding so difficult in T18?

  1. Micrognathia → small mandible → tongue falls back → difficulty latching
  2. CNS malformation → poor suck-swallow-breathe coordination
  3. Cardiac failure → increased caloric demands + fatigue during feeds → failure to thrive
  4. Oesophageal atresia (if present) → cannot swallow at all → surgical consideration
  • For survivors, these therapies aim to:
    • PT: Maintain range of motion (contractures from overlapping fingers, rocker-bottom feet); prevent skin breakdown; respiratory physiotherapy
    • OT: Sensory stimulation; environmental adaptation
    • ST: Oro-motor therapy to optimise feeding function
SymptomManagementRationale
Pain/distressSucrose for procedural pain (neonatal); paracetamol; morphine if severe (palliative dosing)Neonatal pain assessment tools (e.g., NIPS, PIPP-R) guide management; all infants feel pain — comfort is paramount
SecretionsGentle suctioning; glycopyrrolate or hyoscine if excessiveReduces "death rattle" and family distress; improves comfort
SeizuresPhenobarbital (first-line in neonates)Structural brain anomalies → seizure risk; neonatal seizure doses: phenobarbital loading 20 mg/kg IV, maintenance 5 mg/kg/day
ApnoeaPositioning; caffeine (if pursuing active management)Central apnoea from brainstem/cerebellar malformation; caffeine citrate 20 mg/kg loading, 5–10 mg/kg/day maintenance
Respiratory distressOxygen; nasal CPAP if appropriate; avoid intubation/ventilation in comfort careGoal is comfort — supplemental oxygen relieves dyspnoea without invasive measures

3.4 Specific Treatment: Drug, Surgery, Transplantation [7] — Active/Individualised Intervention

This section applies to families who choose active management after thorough counselling.

InterventionIndicationContraindications / Considerations
Pulmonary artery banding (PAB)VSD with pulmonary overcirculation and heart failure in a child selected for interventionLess invasive palliative procedure; reduces pulmonary blood flow without full repair
VSD repairSelected cases with favourable anatomy, surviving beyond neonatal period, family wishes active managementFull cardiopulmonary bypass carries significant risk in a child with multiple comorbidities
PDA ligationHaemodynamically significant PDAMay be done surgically or with catheter-based devices
Valve surgerySevere polyvalvular disease with haemodynamic compromiseTechnically very challenging in a small neonate with myxomatous valves

Evidence: Japanese centres have reported improved survival with cardiac surgery in selected T18 patients (1-year survival increasing from ~5% to ~25% in operated patients). However, this remains controversial — survivors still have profound disability and repeated hospitalisations.

Cardiac Surgery in Trisomy 18 — Evolving Practice

Historically, T18 was considered an absolute contraindication to cardiac surgery. This is no longer universally the case. Current consensus (2024–2026): cardiac surgery may be offered on a case-by-case basis after thorough multidisciplinary discussion and informed family consent. The decision should weigh the severity of cardiac disease, presence of other life-limiting anomalies, family values, and institutional capabilities. In Hong Kong, this would typically involve the paediatric cardiac surgery team at Queen Mary Hospital or Prince of Wales Hospital.

InterventionWhen ConsideredNotes
Supplemental oxygenHypoxia from cardiac defect or central apnoeaLow-flow nasal cannula; non-invasive
Nasal CPAPObstructive or mixed apnoeaMay be appropriate if pursuing active management
Mechanical ventilationGenerally avoided in comfort care; considered in individualised interventionIf intubated, may be very difficult to wean; ethical discussion essential before initiating
TracheostomyRarely — only in survivors with chronic upper airway obstructionSignificant long-term care implications
AnomalySurgical OptionConsideration
Oesophageal atresia / TOFPrimary repair or staged repairT18 significantly worsens the prognosis of OA repair — survival is poor even with surgery; decision depends on goals of care
OmphalocelePrimary closure or staged reduction; or conservative (paint and wait)If comfort care chosen, omphalocele can be managed with topical antiseptic to allow epithelialisation without surgery
Renal anomaliesUsually managed conservativelySurgical intervention rarely indicated given overall prognosis

For survivors beyond the neonatal period:

SystemScreeningFrequency
CardiacEchocardiographyAt diagnosis, then as clinically indicated
GrowthWeight, length, head circumferenceEach visit — use T18-specific growth charts if available
DevelopmentDevelopmental assessmentRegular — expect profound delay; guide early intervention
HearingAuditory brainstem response (ABR) or OAEAt diagnosis; repeat if concerns
VisionOphthalmological examAt diagnosis; annual if surviving
RenalRenal USS + renal functionAt diagnosis; periodic monitoring
OrthopaedicAssessment of contractures, scoliosisAs needed

ComponentDetails
Inheritance / sporadic → recurrence risk [7]Full trisomy (94%): sporadic meiotic non-disjunction → low recurrence risk (~1% above age-related baseline) [1]. Translocation: parental karyotyping essential [2] — if parent is balanced translocation carrier, recurrence risk is significantly higher
Reproductive options [7]Pre-implantation genetic diagnosis (PGD): IVF with embryo biopsy and selection of unaffected embryos — available in Hong Kong. Prenatal diagnosis: CVS or amniocentesis in future pregnancies. NIPT: as screening in subsequent pregnancies. Pre-conception counselling: discussion of maternal age-related risk
Psychosocial supportReferral to support groups (e.g., SOFT — Support Organisation for Trisomy 18, 13, and Related Disorders); bereavement counselling

High Yield — General Management Framework for Chromosomal Disorders

The general management framework for chromosomal abnormalities [7]:

  1. No cure
  2. Supportive: PT, OT, ST
  3. Regular screening for potential comorbidities
  4. Specific treatment: drug, surgery, transplantation (where appropriate)
  5. Genetic counselling: inheritance/sporadic → recurrence risk; reproductive options including pre-implantation genetic diagnosis and prenatal diagnosis

This framework applies to ALL chromosomal disorders (T21, T18, T13, Turner, etc.) — learn it once, apply it universally.

Given that the majority of infants with T18 die within days to weeks, palliative care is central:

ComponentDetails
Palliative care team referralInvolve early — ideally antenatally or at diagnosis
Symptom controlPain, secretions, seizures, respiratory distress — as detailed above
Family supportAllow unlimited family access; facilitate sibling visits; provide private space
Memory makingHand/footprints, photographs, lock of hair, naming ceremony, religious rites
Advance care planningDocument agreed goals of care; "comfort care" or "limited intervention" plan; DNAR (Do Not Attempt Resuscitation) order if appropriate and agreed with family
Bereavement supportCounselling; follow-up contact; support group referral; information about post-mortem examination (offer — helps confirm diagnosis and may aid future counselling)
Post-mortem examinationOffer to family — confirms diagnosis, identifies anomalies not detected in life, provides information for recurrence risk counselling

Ethical Framework — Key Principles

When managing T18, the ethical principles guiding decisions are:

  1. Best interests of the child — the paramount consideration under Hong Kong law
  2. Family autonomy — parents' values and wishes are central to decision-making
  3. Proportionality — interventions should be proportionate to expected benefit
  4. Non-maleficence — avoid causing unnecessary suffering
  5. Shared decision-making — the medical team provides information and recommendations; the family makes the decision

In cases of disagreement between team and family, involve clinical ethics committee and consider legal advice.

PhaseKey Actions
AntenatalGenetic counselling; reproductive options (termination / continuation); birth plan; delivery mode (vaginal preferred); serial USS monitoring
Delivery roomBased on pre-agreed plan; thermoregulation; gentle airway management; family bonding; FISH for confirmation
NeonatalGoals of care discussion; organ assessment (echo, renal USS, cranial USS); feeding support; symptom management; palliative care referral
SurvivorsSupportive: PT, OT, ST [7]; regular screening for comorbidities [7]; specific treatment as appropriate [7]; developmental support
GeneticParental karyotyping if translocation [2]; genetic counselling: recurrence risk + reproductive options (PGD, prenatal diagnosis) [7]
End of lifeComfort care; symptom control; family support; memory making; bereavement support; offer post-mortem

High Yield Summary — Management of Trisomy 18

  1. No cure [7] — management is supportive + symptomatic + genetic counselling
  2. General framework [7]: Supportive (PT, OT, ST) → Regular screening for comorbidities → Specific treatment (drug, surgery) → Genetic counselling (recurrence risk, PGD, prenatal diagnosis)
  3. Goals of care: Individualised, family-centred — spectrum from comfort care to selected intervention
  4. Antenatally: Non-directive counselling; termination or continuation; vaginal delivery preferred; CS not for fetal indication alone
  5. Cardiac surgery: No longer absolute contraindication — case-by-case decision after MDT discussion
  6. Feeding: Oral → NG → gastrostomy (graduated approach depending on goals)
  7. Palliative care: Central to management — symptom control, family bonding, memory making, bereavement support
  8. Genetic counselling: Low recurrence risk for full trisomy; parental karyotyping essential for translocation type; reproductive options: PGD and prenatal diagnosis [7]

Active Recall — Management of Trisomy 18

References

[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pp. 505–506) [2] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 838) [7] Senior notes: Maksim Paediatric Notes.pdf (pp. 202–204) — General investigation and management framework for genetic/chromosomal disorders

Complications of Edward Syndrome (Trisomy 18)

The complications of Trisomy 18 are not truly "complications" in the conventional sense (i.e., unexpected adverse events arising from a disease or its treatment). Rather, they are the inevitable consequences of the multi-system organ malformations inherent to the syndrome. Because cardiac defects are present in ~100% [1], cerebellar hypoplasia in 32% [1], and renal anomalies are common [1], the complications are predictable and progressive.

The complications can be organised into:

  1. Direct complications of congenital malformations (cardiac, neurological, renal, GI)
  2. Complications of the overall condition (growth failure, infections, death)
  3. Complications of treatment (iatrogenic — relevant when active intervention is pursued)
  4. Psychosocial and family complications
  5. Rare long-term complications (relevant to the small minority of survivors)

Cardiac defects are present in virtually 100% of T18 infants [1] and are the leading cause of morbidity and mortality.

ComplicationPathophysiologyClinical Manifestation
Congestive heart failure (CHF)VSD (94%) [1] → left-to-right shunt → pulmonary overcirculation → volume overload of left heart → CHF. Additionally, myxomatous change of valves [1] → valvular regurgitation → further volume overloadTachypnoea, tachycardia, hepatomegaly, poor feeding, diaphoresis during feeds, failure to thrive
Pulmonary hypertension (pHTN)Large unrepaired VSD → chronic excessive pulmonary blood flow → shear stress damages pulmonary arterioles → progressive pulmonary vascular remodelling → irreversible pulmonary arterial hypertensionWorsening cyanosis, loud P2 on auscultation, right ventricular heave
Eisenmenger syndromeEnd-stage of untreated large L-to-R shunt: pulmonary vascular disease → reversal of shunt → R-to-L → cyanosis [11]. Triad: congenital L-to-R shunt + pulmonary arterial disease + cyanosisCentral cyanosis, digital clubbing, loss of previously audible VSD murmur (because shunt gradient equalises), exertional dyspnoea, reactive erythrocytosis [11]
Infective endocarditis (IE)Turbulent flow across structural cardiac defects → endothelial damage → bacterial seeding during transient bacteraemiaFever, new/changing murmur, embolic phenomena — however, given the short survival, IE is uncommon
ArrhythmiasStructural cardiac abnormalities + myxomatous valves → abnormal conduction pathways; polyvalvular disease → chamber dilation → substrate for arrhythmiaBradycardia, supraventricular tachycardia, heart block

Why is CHF so common and so early? In a normal neonate, pulmonary vascular resistance (PVR) is high at birth and falls gradually over the first weeks. As PVR falls, the left-to-right shunt across the VSD increases → pulmonary overcirculation develops → CHF manifests at 4–8 weeks of life. In T18, this is the typical timeline — but the infant's overall fragility (IUGR, poor feeding, CNS impairment) means they tolerate heart failure very poorly.

Eisenmenger Syndrome in T18 — Theoretical vs Clinical

In practice, most T18 infants die before Eisenmenger syndrome develops (which typically takes months to years of unrepaired shunt). However, in the rare survivors — particularly those with mosaic T18 or those not offered cardiac repair — Eisenmenger physiology can develop. Once established, it is irreversible and contraindicates cardiac repair [11]. The only curative option at that stage is heart-lung transplantation [11], which is not offered in T18.

ComplicationPathophysiologyClinical Manifestation
SeizuresStructural brain abnormalities (cerebellar hypoplasia (32%) [1], cortical malformations) → abnormal neuronal connectivity → epileptogenicityNeonatal seizures (subtle, tonic, clonic); recurrent seizures in survivors
Central apnoeaBrainstem and cerebellar malformation → impaired central respiratory drive → periodic breathing progressing to apnoeic episodesApnoeic episodes, desaturations, bradycardic events; often the terminal event
Profound intellectual disabilityGlobal cortical developmental impairment from gene dosage imbalance → failure to achieve any developmental milestonesNo purposeful interaction in severe cases; may have limited social responsiveness in milder (mosaic) cases [12]
Feeding incoordinationCNS dysfunction → poor suck-swallow-breathe reflex coordinationChoking, aspiration, failure to establish oral feeding
Aspiration pneumoniaSecondary to feeding incoordination (above) + micrognathia → pooling of secretions + gastro-oesophageal refluxRecurrent respiratory infections, consolidation on CXR

Why is central apnoea so important? Central apnoea is often the proximate cause of death in T18. The brainstem respiratory centres are malformed → the infant simply stops breathing. This can occur unpredictably, even in otherwise "stable" infants. Families must be counselled about this.

ComplicationPathophysiologyClinical Manifestation
Severe failure to thriveMulti-factorial: (1) intrinsic growth impairment from gene dosage imbalance; (2) CHF → increased metabolic demands + poor intake; (3) feeding difficulties (micrognathia, poor suck); (4) malabsorption (GI anomalies)Weight, length, and head circumference all severely below normal centiles
Gastro-oesophageal reflux (GOR)Oesophageal dysmotility + hypotonia → incompetent lower oesophageal sphincter → acid refluxVomiting, irritability, aspiration events
Necrotising enterocolitis (NEC)Premature/IUGR neonates + cardiac disease (low cardiac output → mesenteric hypoperfusion) → ischaemic bowel injuryAbdominal distension, bilious vomiting, bloody stools, pneumatosis on AXR

ComplicationPathophysiologyClinical Manifestation
Renal failureRenal anomalies [1] — horseshoe kidney, hydronephrosis, renal agenesis → impaired renal functionOliguria, elevated creatinine, electrolyte derangement
Urinary tract infections (UTIs)Structural renal anomalies → urinary stasis → predisposition to ascending infectionsFever, poor feeding, sepsis in neonates
Obstructive uropathyHydronephrosis / ureteropelvic junction obstruction → ureteral dilation → progressive renal damage if untreatedPalpable flank mass, recurrent UTIs

ComplicationPathophysiologyClinical Manifestation
Recurrent respiratory infectionsPoor cough reflex (CNS impairment) + aspiration + cardiac failure (pulmonary congestion) → ideal environment for bacterial colonisationPneumonia, bronchiolitis, respiratory failure
SepsisOverall immune immaturity (IUGR, prematurity) + invasive procedures (NG tubes, IV lines) + poor skin integrityNeonatal sepsis, late-onset sepsis
Otitis mediaCraniofacial anomalies (dysplastic ears, abnormal eustachian tube anatomy) → impaired middle ear drainageRecurrent ear infections, conductive hearing loss

ComplicationPathophysiologyClinical Manifestation
Oesophageal atresia / TOFDevelopmental failure of tracheo-oesophageal separation; T18 is associated with OA/TEF [3]Unable to swallow; drooling; "can't pass NG tube"; aspiration of secretions
Omphalocele complicationsMidline closure defect → herniated viscera → risk of rupture, infection, bowel ischaemia [3][10]Visible omphalocele at birth; if ruptured → exposed bowel → emergency surgical coverage
Malrotation with volvulusAbnormal intestinal rotation during embryogenesis → abnormal mesenteric attachment → risk of midgut volvulusBilious vomiting (surgical emergency), abdominal distension
Feeding intoleranceGI dysmotility + GOR + structural anomaliesVomiting, abdominal distension, poor weight gain

ComplicationPathophysiologyClinical Manifestation
Progressive joint contracturesAbnormal muscle tone + limited movement + connective tissue abnormalities → progressive shortening of tendons and ligamentsWorsening fixed flexion deformities of fingers, wrists, hips
ScoliosisVertebral anomalies + hypotonia → abnormal spinal curvatureVisible truncal asymmetry; may worsen respiratory function
Skin breakdownPoor nutrition + immobility + thin skin → pressure injuriesPressure ulcers over bony prominences

ComplicationPathophysiologyClinical Manifestation
Congenital cataractEdward syndrome is a recognised syndromal cause of congenital cataract [6] — lens opacification from abnormal lens fibre developmentLeukocoria (white pupil), failure of visual fixation
Corneal opacityAnterior segment dysgenesisVisible corneal clouding

For the ~5% who survive beyond 1 year [1] (typically mosaic or partial trisomy cases):

ComplicationDetails
HepatoblastomaEdward syndrome is a recognised association for hepatoblastoma [10] — the most common primary liver malignancy in early childhood. Although rare, screening with periodic AFP levels and abdominal USS may be considered in survivors
Wilms tumourRare association with Trisomy 18; renal anomalies may predispose
Chronic lung diseaseFrom recurrent aspiration, recurrent infections, and pulmonary overcirculation
Chronic constipationGI dysmotility
Hearing lossConductive (from recurrent otitis media + ear dysplasia) and/or sensorineural

Hepatoblastoma and Trisomy 18

Edward syndrome (Trisomy 18) is listed among the associated syndromes for hepatoblastoma [10], alongside Beckwith-Wiedemann, FAP, Down syndrome, and Li-Fraumeni. This is a rare but testable association in exam settings. In survivors, clinicians should maintain a low threshold for investigating hepatomegaly or rising AFP.

When active intervention is pursued, the following iatrogenic complications may arise:

InterventionPotential Complications
Cardiac surgeryPerioperative mortality (very high in T18); bleeding; infection; difficulty weaning from bypass; post-operative heart failure; arrhythmias
Mechanical ventilationVentilator-associated pneumonia; air leak (pneumothorax); difficulty weaning → chronic ventilator dependence; tracheal injury
GastrostomyWound infection; tube displacement; GOR worsening; aspiration
OA/TOF repairAnastomotic leak; stricture; recurrent TOF; GOR; tracheomalacia
Omphalocele repairAbdominal compartment syndrome (from ↑ intra-abdominal pressure) → difficult ventilation, ↓venous return, ↓urine output [3]

These are often underappreciated but are critical in family-centred paediatric care:

ComplicationDetails
Parental grief and bereavementAnticipatory grief (antenatal diagnosis); complicated grief after death; feelings of guilt, anger, isolation
Sibling impactSiblings may feel neglected, confused, or frightened; age-appropriate communication is essential
Relationship strainDisagreements between parents about goals of care; financial stress from hospital stays
Decision-making burdenParents may experience lasting distress about decisions made (whether to intervene or not); ongoing support is essential
Mental healthParental depression, anxiety, post-traumatic stress disorder (PTSD); screen and refer
Impact on future reproductive decisionsAnxiety about future pregnancies; need for ongoing genetic counselling and reassurance about recurrence risk

Understanding the proximate causes of death is important for counselling families:

CauseMechanismFrequency
Central apnoeaBrainstem/cerebellar malformation → cessation of respiratory driveMost common
Cardiac failureProgressive CHF from unrepaired VSD + valvular diseaseVery common
Respiratory failureAspiration pneumonia, pulmonary overcirculation, pulmonary hypoplasiaCommon
SepsisSecondary to aspiration, UTI, or line-related infectionCommon
Multiorgan failureCumulative effect of cardiac, renal, and CNS dysfunctionTerminal pathway

High Yield Summary — Complications of Trisomy 18

  1. Leading cause of death: Central apnoea (brainstem malformation) and cardiac failure (VSD + polyvalvular disease)
  2. Cardiac: CHF → pulmonary hypertension → Eisenmenger (if survives long enough); arrhythmias; IE (rare)
  3. Neurological: Seizures, central apnoea, profound intellectual disability, feeding incoordination → aspiration
  4. Growth: Severe failure to thrive (multi-factorial: cardiac, feeding, intrinsic growth impairment)
  5. Renal: Renal failure from structural anomalies; recurrent UTIs
  6. GI: OA/TOF; omphalocele complications; malrotation/volvulus; GOR → aspiration
  7. Infectious: Recurrent respiratory infections, sepsis, otitis media
  8. Ophthalmological: Congenital cataract [6]
  9. Rare/long-term: Hepatoblastoma [10] (testable association); Wilms tumour; chronic lung disease
  10. Iatrogenic: Post-surgical complications (cardiac, GI)
  11. Psychosocial: Parental grief, sibling impact, decision-making burden, mental health
  12. Prognosis: median survival 14 days; only 5% reach 1 year [1]

Active Recall — Complications of Trisomy 18

References

[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pp. 505–506) [3] Senior notes: Maksim Surgery Notes.pdf (pp. 331, 333) — Oesophageal atresia, omphalocele, and associated conditions [6] Senior notes: Ryan Ho Opthalmology.pdf (p. 122) — Congenital cataract syndromal associations including Edward syndrome [10] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (p. 1077) — Hepatoblastoma associations including Trisomy 18 [11] Senior notes: Ryan Ho Cardiology.pdf (p. 186) — Eisenmenger syndrome [12] Senior notes: Ryan Ho Psychiatry.pdf (p. 244) — Intellectual disability and Trisomy 18

High Yield Summary

Edward Syndrome (Trisomy 18) — Pre-DDx/Dx/Mx Summary

  1. Definition: Extra chromosome 18 → lethal chromosomal abnormality
  2. Epidemiology: 2nd most common autosomal trisomy; 1/3,000–1/15,000 live births; F > M (4:1); increases with maternal age
  3. Genetics: ~94% full trisomy (meiotic non-disjunction), ~5% mosaic (mitotic error), ~1% translocation (familial risk)
  4. Cardinal clinical features:
    • Microcephaly with prominent occiput
    • Clenched fists with overlapping fingers (2nd over 3rd, 5th over 4th) — 95%
    • Rocker-bottom feet — 90%
    • Cardiac defects in ~100%, most commonly VSD (94%) and polyvalvular myxomatous disease
    • Low birth weight (> 90%)
    • Cerebellar hypoplasia (most common CNS anomaly)
  5. Prognosis: Median survival = 14 days; only 5% survive to 1 year
  6. Recurrence: Low, unless parental balanced translocation → always offer parental karyotyping
  7. Distinguish from T21: Prominent occiput (T18) vs flat occiput (T21); clenched fists (T18) vs single palmar crease (T21)
  8. Distinguish from T13: T13 classical triad = microphthalmos + cleft lip/palate + polydactyly

High Yield Summary — Diagnosis of Trisomy 18

  1. Clinical suspicion: Pattern of prominent occiput + clenched fists (2nd over 3rd, 5th over 4th) + rocker-bottom feet + VSD + IUGR
  2. Antenatal screening: NIPT (> 95% detection rate); first-trimester combined screening (both PAPP-A and free β-hCG are LOW in T18)
  3. Antenatal confirmation: CVS (11–14 weeks) or amniocentesis (≥15 weeks) → karyotype/CMA
  4. Postnatal confirmation: Urgent FISH (24–48h) + full G-banded karyotype (7–14 days) from peripheral blood
  5. Concurrent organ assessment: Echocardiography (VSD ~94%), renal USS, cranial USS, ophthalmology
  6. Parental karyotyping: Essential when translocation type identified — determines recurrence risk
  7. Three types: Full trisomy (94%) vs mosaic (5%) vs translocation (1%) — karyotype distinguishes them

High Yield Summary — Management of Trisomy 18

  1. No cure [7] — management is supportive + symptomatic + genetic counselling
  2. General framework [7]: Supportive (PT, OT, ST) → Regular screening for comorbidities → Specific treatment (drug, surgery) → Genetic counselling (recurrence risk, PGD, prenatal diagnosis)
  3. Goals of care: Individualised, family-centred — spectrum from comfort care to selected intervention
  4. Antenatally: Non-directive counselling; termination or continuation; vaginal delivery preferred; CS not for fetal indication alone
  5. Cardiac surgery: No longer absolute contraindication — case-by-case decision after MDT discussion
  6. Feeding: Oral → NG → gastrostomy (graduated approach depending on goals)
  7. Palliative care: Central to management — symptom control, family bonding, memory making, bereavement support
  8. Genetic counselling: Low recurrence risk for full trisomy; parental karyotyping essential for translocation type; reproductive options: PGD and prenatal diagnosis [7]

High Yield Summary — Complications of Trisomy 18

  1. Leading cause of death: Central apnoea (brainstem malformation) and cardiac failure (VSD + polyvalvular disease)
  2. Cardiac: CHF → pulmonary hypertension → Eisenmenger (if survives long enough); arrhythmias; IE (rare)
  3. Neurological: Seizures, central apnoea, profound intellectual disability, feeding incoordination → aspiration
  4. Growth: Severe failure to thrive (multi-factorial: cardiac, feeding, intrinsic growth impairment)
  5. Renal: Renal failure from structural anomalies; recurrent UTIs
  6. GI: OA/TOF; omphalocele complications; malrotation/volvulus; GOR → aspiration
  7. Infectious: Recurrent respiratory infections, sepsis, otitis media
  8. Ophthalmological: Congenital cataract [6]
  9. Rare/long-term: Hepatoblastoma [10] (testable association); Wilms tumour; chronic lung disease
  10. Iatrogenic: Post-surgical complications (cardiac, GI)
  11. Psychosocial: Parental grief, sibling impact, decision-making burden, mental health
  12. Prognosis: median survival 14 days; only 5% reach 1 year [1]

Patau Syndrome (trisomy 13)

Patau syndrome is a severe chromosomal disorder caused by an extra copy of chromosome 13, presenting at birth with holoprosencephaly, cleft lip/palate, polydactyly, and major cardiac defects, with most affected infants dying within the first year of life.

Down Syndrome (trisomy 21)

Down syndrome is a genetic condition caused by the presence of an extra copy of chromosome 21, typically apparent from birth, resulting in characteristic facial features, intellectual disability of variable degree, and associated congenital anomalies such as cardiac defects.

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