Asymmetrical Fetal Growth Restriction

Asymmetrical fetal growth restriction is a fetus whose abdominal circumference is smaller than its head circumference, giving a raised head to abdomen ratio. It results from placental insufficiency in the third trimester, which diverts blood to the brain and reduces liver glycogen and fat. It matters because it is the commonest form, it is detectable on ultrasound, and timed delivery lowers stillbirth.

• Placental disease is the usual cause.
• Risk factors: preeclampsia, chronic hypertension, smoking, anaemia, malaria, sickle cell disease, thrombophilia, antiphospholipid syndrome, kidney disease.
• Often shows reduced liquor and abnormal Doppler.

Fundal height falls behind dates in the third trimester, with reduced fetal movements and sometimes hypertension and proteinuria. Fetal heart sounds are usually normal until late disease.

• Small abdomen with a relatively large head on scan.
• Reduced liquor volume.
• Differential diagnosis: constitutionally small fetus, wrong dates, symmetrical growth restriction, oligohydramnios from membrane rupture, congenital infection, fetal anomaly.
• Complications: stillbirth, fetal hypoxia and acidosis, preterm birth, hypoglycaemia, hypothermia, polycythaemia, neonatal death, later cardiovascular disease.

The approach is serial growth scans with Doppler assessment.

• Ultrasound: abdominal circumference below the 10th centile or falling across centiles, head to abdomen ratio above the 95th centile, estimated fetal weight below the 10th centile.
• Umbilical artery Doppler (pulsatility index above the 95th centile, absent or reversed end diastolic flow), middle cerebral artery pulsatility index below the 5th centile, cerebroplacental ratio below the 5th centile.
• Deepest vertical pocket below 2 cm; uterine artery Doppler.
• Maternal: blood pressure, urine protein to creatinine ratio, full blood count, malaria rapid test, antiphospholipid antibodies, glucose.

The principle is to treat the cause, monitor with Doppler and cardiotocography and deliver at the gestation set by the Doppler stage.

• Supportive: rest; left lateral position; stop smoking; fetal movement counts; admit when absent end diastolic flow, reduced movements or hypertension.
• Pharmacological: labetalol 200 mg oral every 8 to 12 hours (maximum 2.4 g daily) or nifedipine modified release 30 to 60 mg oral once daily (maximum 120 mg) for blood pressure 140/90 mmHg or more; ferrous sulphate 200 mg oral 8-hourly; enoxaparin 40 mg subcutaneous daily with aspirin 150 mg oral at night for antiphospholipid syndrome; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days when delivery within 7 days is likely; magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most for delivery before 32 weeks; aspirin 150 mg oral at night from 12 weeks to 36 weeks in the next pregnancy.
• Procedures: delivery at 37 weeks if the umbilical artery Doppler is normal, 34 weeks for absent end diastolic flow, 30 to 32 weeks for reversed flow; caesarean section when Dopplers are abnormal; induction with misoprostol 25 micrograms vaginal 6-hourly (maximum 4 doses) or Foley catheter for normal Dopplers with continuous cardiotocography.
• Special groups: preeclampsia needs magnesium sulphate for severe features; newborns feed within 30 minutes and have glucose and haematocrit checked, with glucose below 2.6 mmol/L treated by dextrose 10 percent 2 mL/kg IV over 10 minutes then 80 mL/kg per day.
• Red flags: reduced fetal movements, absent or reversed end diastolic flow, abnormal cardiotocography, oligohydramnios, severe hypertension.
• Follow-up: umbilical artery Doppler weekly (twice weekly if abnormal); cardiotocography twice weekly to daily by stage; postnatal review of newborn weight and feeding.