Intrauterine Growth Restriction

Failure of the fetus to reach its genetically determined growth potential, most commonly from placental insufficiency, distinguished from a small for gestational age (SGA) fetus that is constitutionally small but growing appropriately along its own centile.

• Early-onset FGR (before 32 weeks) is typically severe and placental, often associated with pre-eclampsia and abnormal umbilical artery Doppler.

• Late-onset FGR (after 32 weeks) is more subtle, with a milder placental insufficiency pattern, and is more often missed on routine assessment.

Reduced fundal height for gestational age on serial measurement (symphysis-fundal height), reduced fetal movements, and, in established growth restriction, oligohydramnios (a marker of chronic placental insufficiency, see that entry). Often clinically silent until identified on scan.

• Estimated fetal weight or abdominal circumference below the 10th centile on ultrasound is the standard threshold for SGA/FGR classification, with severe FGR generally defined as below the 3rd centile
• Umbilical artery Doppler is central to distinguishing placental FGR from constitutionally small: absent or reversed end-diastolic flow indicates significant placental compromise and is an indication for expedited delivery
• Middle cerebral artery Doppler (brain-sparing pattern, reflecting fetal redistribution of blood flow to protect the brain) and ductus venosus Doppler (abnormal a-wave reflecting more advanced cardiac compromise) are used for further risk stratification, particularly in late-onset FGR
• Screening for underlying causes: maternal BP and urine protein (pre-eclampsia), infection screen (TORCH where clinically indicated), and detailed anomaly scan/karyotyping if structural anomaly or aneuploidy is suspected
• Uterine artery Doppler at the 20 week anomaly scan can identify women at higher risk of later FGR

• Aspirin 75 to 150 mg PO od from 12 weeks in future pregnancies for women with risk factors, given the shared pathophysiology with pre-eclampsia (see Pre-eclampsia entry)
• Serial growth scans and Doppler assessment, frequency guided by severity, ranging from every 2 weeks in milder cases to twice weekly or more in severe, early-onset FGR with abnormal Doppler
• Corticosteroids for fetal lung maturation if preterm delivery is anticipated
• Magnesium sulfate for neuroprotection if delivery under roughly 30 to 32 weeks is anticipated
• Delivery timing is individualized based on Doppler findings, gestation, and CTG: absent end-diastolic flow generally prompts delivery by around 32 to 34 weeks (earlier with reversed flow or other severe features), while milder late-onset FGR with normal Doppler may be managed to closer to term with increased surveillance
• Mode of delivery guided by severity, cesarean section is more likely with significant placental compromise given reduced fetal tolerance of labor

Referral: fetal medicine specialist input for severe or early-onset FGR, or abnormal Doppler findings.