Fetal growth restriction and small-for-gestational-age infant — viva

Stem

The examiner hands you the antenatal summary of a 36-week infant: birthweight 2100 g (below the 3rd centile), maternal pre-eclampsia, absent end-diastolic flow on the umbilical artery Doppler, and a wasted neonate now in the nursery. [1]

Examiner: What is your opening approach to this infant? [1]

Strong answer: I would first classify this as fetal growth restriction rather than constitutional smallness, because the antenatal Doppler is abnormal and the infant is wasted. I would plot the weight, length and head circumference on a gestation- and sex-specific INTERGROWTH-21st chart, calculate the Ponderal Index, and judge symmetry. Then I would pre-empt the four neonatal complications — hypothermia, hypoglycaemia, polycythaemia and feeding difficulty — from the first feed, with warmth, early feeding, scheduled glucose monitoring and a selective haematocrit. [3] [7]

Branch 1 — Classification

Examiner: How do you distinguish SGA from FGR, and symmetric from asymmetric? [2]

Strong answer: SGA is a size descriptor below the 10th centile; FGR is a pathological failure to reach growth potential. They overlap but are not synonymous: a constitutionally small infant is healthy and not growth-restricted, and a growth-restricted fetus may not yet be below the 10th centile if its velocity has just fallen. Symmetric restriction (head, length and weight all small) points to an early intrinsic cause such as chromosome or infection; asymmetric restriction (head spared, body wasted) reflects brain-sparing placental insufficiency. [6]

Examiner probe: What would change your workup? [2]

Strong answer: Dysmorphism, a structural anomaly, organomegaly, petechiae or a rash would shift me toward a chromosomal or congenital infection pathway, prompting karyotype or microarray and a congenital infection screen rather than a pure placental-insufficiency workup. [6]

Branch 2 — Surveillance and prognosis

Examiner: What does an abnormal umbilical artery Doppler tell you about prognosis? [4]

Strong answer: Absent or reversed end-diastolic flow marks severe placental insufficiency and a fetus at high risk of stillbirth and perinatal compromise; it drives intensified surveillance and decisions about delivery timing. Outcome depends on cause, severity, gestation and the degree of Doppler abnormality, not on size alone. [4]

Examiner probe: What should you counsel the family about long-term? [5]

Strong answer: I would counsel honestly that severe early FGR carries a real risk of mortality, neurodevelopmental impairment and cerebral palsy, and that fetal growth restriction is now recognised as an origin of adult cardiovascular and metabolic disease through fetal reprogramming. I would frame follow-up as part of treatment: growth monitoring, neurodevelopmental surveillance, and vision and hearing checks if very preterm. [5]

Branch 3 — A trap

Examiner: The registrar says the baby cannot be growth-restricted because it is still on the 12th centile. How do you respond? [1]

Strong answer: I would correct that. Fetal growth restriction is a pathological process, not a centile threshold. A fetus whose growth has fallen across centiles — for example from the 60th to the 12th — is growth-restricted even though it never crossed the 10th, because its velocity has failed and placental insufficiency may be present. I would make the decision on velocity, Doppler and proportionality, not on the absolute centile alone. [1]