Fetal growth restriction and small for gestational age

A 28-year-old woman is referred at 29 weeks with an estimated fetal weight on the 3rd centile and an umbilical artery pulsatility index above the 95th. The growth scan has just handed you the single most preventable cause of stillbirth, and what you do next — the surveillance interval, the Doppler interpretation, the timing of delivery — is the difference between a healthy baby and a perinatal mortality meeting. Fetal growth restriction is one of the highest-yield topics in the fellowship exam because it joins ultrasound, Doppler physiology, three landmark trials and a judgement about timing into one station. ^[1]

Overview and definition

The first distinction the examiner wants is between small for gestational age (SGA) and fetal growth restriction (FGR). They are not the same thing. ^[1]

• SGA is a size: a birthweight or estimated fetal weight below the 10th centile for gestation. Many SGA babies are constitutionally small and healthy. ^[1]
• FGR is a pathology: the failure of a fetus to reach its growth potential because of an underlying cause (usually placental insufficiency). An FGR fetus is at increased risk of stillbirth, neonatal morbidity and long-term impairment.

The Gordijn 2016 Delphi consensus resolved the historical confusion between the two by giving you reproducible criteria for early and late FGR — and these are the definitions to hold cold.^[1]