Preterm Birth Due to Fetal Growth Restriction

Preterm birth due to fetal growth restriction is delivery before 37 weeks because placental failure threatens the fetus, shown by abnormal umbilical artery Doppler, abnormal ductus venosus flow or a pathological heart rate tracing. It results from placental vascular disease, often with preeclampsia. It matters because delivery too early adds prematurity, and delivery too late risks stillbirth and brain injury, so timing follows the Doppler stage.

• Absent end diastolic flow suggests delivery at about 34 weeks and reversed flow at 30 to 32 weeks.
• Risk factors: preeclampsia, chronic hypertension, antiphospholipid syndrome, kidney disease, smoking, malaria, anaemia.
• Babies have a higher risk of hypoglycaemia, hypothermia, polycythaemia and necrotising enterocolitis.

Women have a small fundal height, reduced fetal movements and sometimes hypertension and proteinuria. Many have no symptoms and the indication comes from scans.

• Fundal height 3 cm or more below dates.
• Oligohydramnios.
• Differential diagnosis: constitutionally small fetus, wrong dates, chromosomal abnormality, congenital infection, placental abruption, preeclampsia without growth restriction.
• Complications: stillbirth, fetal acidosis, intraventricular haemorrhage, necrotising enterocolitis, neonatal hypoglycaemia, polycythaemia, cerebral palsy, neonatal death, maternal preeclampsia.

The approach is serial Doppler and cardiotocography to stage the disease and time birth.

• Ultrasound: estimated fetal weight or abdominal circumference below the 3rd centile, or below the 10th with abnormal Doppler; umbilical artery pulsatility index, absent or reversed end diastolic flow; middle cerebral artery pulsatility index; cerebroplacental ratio; ductus venosus Doppler (absent or reversed a wave); deepest pocket.
• Cardiotocography once or twice daily; computerised short term variation below 3.5 ms before 32 weeks where available.
• Maternal blood pressure, urine protein to creatinine ratio, platelets, liver enzymes, creatinine, antiphospholipid antibodies, malaria test, syphilis and HIV tests.
• Amniocentesis for karyotype and cytomegalovirus PCR if an anomaly or symmetrical growth restriction is found.

The principle is to admit, give steroids and magnesium sulphate, and deliver at the Doppler stage.

• Supportive: admit from 26 weeks for absent or reversed end diastolic flow; left lateral rest; Doppler twice weekly and cardiotocography once or twice daily; daily fetal movement counts; transfer to a unit with neonatal intensive care; counselling about outcome before 26 weeks.
• Pharmacological: betamethasone 12 mg IM twice, 24 hours apart, between 24 weeks and 34 weeks and 6 days; magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most, before 32 weeks (stop for absent patellar reflexes, respiratory rate below 12 per minute or urine below 30 mL per hour, with calcium gluconate 1 g IV over 10 minutes for toxicity); 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 of 140/90 mmHg or more; enoxaparin 40 mg subcutaneous daily with aspirin 150 mg oral at night for antiphospholipid syndrome; oxytocin 10 IU IM at birth; newborn dextrose 10 percent 2 mL/kg IV over 10 minutes then 80 mL/kg per day for glucose below 2.6 mmol/L.
• Procedures: caesarean section at 34 weeks for absent end diastolic flow and at 30 to 32 weeks for reversed flow, and at once for abnormal ductus venosus or pathological cardiotocography; induction at 37 weeks for normal Doppler with continuous cardiotocography; partial exchange transfusion in the newborn for haematocrit above 65 percent.
• Special groups: severe preeclampsia needs magnesium sulphate 4 g then 1 g per hour for 24 hours after birth and labetalol 20 mg IV then 40 mg, 80 mg and 80 mg at 10 minute intervals (maximum 220 mg) for blood pressure of 160/110 mmHg or more; newborns need warmth, kangaroo mother care, and breast milk feeding in small amounts to protect the gut.
• Red flags: reversed end diastolic flow, abnormal ductus venosus, pathological cardiotocography, absent fetal movements, severe hypertension, bleeding.
• Follow-up: Doppler twice weekly; daily cardiotocography after admission; neonatal intensive care follow-up and developmental review at 2 years; aspirin 150 mg oral at night from 12 weeks to 36 weeks in the next pregnancy.