Late‑Onset Fetal Growth Restriction: Evidence‑Based Guidelines

Diagnostic Criteria

The International Consensus on Fetal Growth Restriction defines late‑onset FGR (≥ 32 weeks) by an abdominal circumference < 5th percentile and a cerebro‑placental ratio < 5th percentile; the presence of both parameters confirms the diagnosis【1】.
Combining these two contributory parameters (AC < 5th pct and CPR < 5th pct) is required to label a fetus as having late‑onset FGR according to the consensus definition【1】.

An abdominal circumference at the 5th percentile together with an abnormal CPR indicates pathologic smallness rather than normal variation【1】.
Simple small‑for‑gestational‑age (SGA) refers to fetuses < 10th percentile without evidence of placental dysfunction and with near‑normal perinatal outcomes; the abnormal CPR demonstrates placental insufficiency, thereby excluding simple SGA【1】.

Early‑onset FGR is diagnosed before 32 weeks gestation; a fetus identified at exactly 32 weeks falls under the late‑onset category【4】.
Early‑onset FGR (< 32 weeks) is associated with severe placental dysfunction, abnormal umbilical artery and venous Doppler waveforms, a strong link to maternal hypertensive disorders, and extensive placental histopathology【4】.
Late‑onset FGR accounts for roughly 70–80 % of all FGR cases, tends to be milder, shows predominant cerebral Doppler abnormalities, and exhibits less extensive placental under‑perfusion【4】.

Umbilical artery Doppler should be performed every 1–2 weeks initially; if Doppler findings remain stable, the interval can be extended to every 2–4 weeks【6】.
Cardiotocography is recommended weekly to assess fetal well‑being【6】.
Biometric measurements (e.g., abdominal circumference) should be repeated every 2 weeks to evaluate growth velocity【6】.
Middle cerebral artery (MCA) Doppler and CPR monitoring every 2 weeks is advised because the CPR is already abnormal【1】【2】.

When the umbilical artery Doppler remains normal, delivery is recommended at 37–38 weeks gestation for late‑onset FGR with abnormal CPR【1】【2】【6】.
If the umbilical artery Doppler becomes abnormal (e.g., > 95th percentile), delivery should be planned by 37–38 weeks gestation【1】【2】.

Relying solely on umbilical artery Doppler is insufficient to distinguish late‑onset FGR from constitutional SGA; the CPR provides greater sensitivity for detecting placental insufficiency in late‑onset cases【1】.
An amniotic fluid deepest vertical pocket of 2 cm, while technically within the normal range, lies at the lower threshold and warrants continued monitoring rather than being considered reassuring【7】.