Fetal growth restriction: small is not always simple

Direct answer

Fetal growth restriction (FGR) means that a fetus may not be reaching its growth potential because of a maternal, fetal, or placental problem. A fetus can measure small and still be healthy, while another fetus near or above a conventional centile threshold may show a concerning slowing of growth or abnormal placental blood flow. Assessment therefore cannot rely on one estimated fetal weight alone.

The first questions are whether pregnancy dating is reliable, whether the measurements are technically sound, whether anatomy is normal, and whether growth has changed over time. The clinical meaning also depends on gestational age: severe early FGR has a different differential diagnosis and risk profile from mild late-onset smallness.

What the MFM assessment checks

Evaluation commonly includes a detailed review of fetal biometry, amniotic fluid, placental appearance, and umbilical artery Doppler. Depending on the presentation and local guideline, additional Doppler or surveillance methods may be used. Maternal blood pressure, symptoms, laboratory results, medical disease, smoking or medication exposure, and previous pregnancy history can provide essential context.

Early or severe FGR, FGR associated with an abnormality, or unexplained FGR may prompt discussion of genetic testing or selected infection testing. Testing should be targeted to the phenotype and evidence; broad panels without a clinical rationale can create confusing results without improving care.

Surveillance and delivery decisions

Once FGR is diagnosed, the plan balances two competing risks: remaining in a pregnancy with deteriorating placental function and delivering too early. The frequency of growth scans, Doppler, cardiotocography, or other surveillance depends on severity, gestational age, Doppler findings, maternal disease, and the resources available.

Delivery timing is not determined by estimated weight alone. It may change with absent or reversed end-diastolic flow, worsening maternal hypertension, reduced fetal movements, abnormal fetal testing, poor interval growth, or other deterioration. Very preterm cases require coordination with neonatology and a hospital equipped for the expected maternal and newborn needs.

What to bring and when to seek help

Bring the earliest dating scan, every growth report, the original images when available, blood-pressure records, medication list, and relevant laboratory results. Seek immediate assessment for reduced fetal movements, heavy bleeding, severe abdominal pain, fluid loss, severe headache with visual symptoms, or feeling acutely unwell; do not wait for the next growth appointment.