Small-for-Gestational-Age Fetus

A small for gestational age fetus has an estimated fetal weight or abdominal circumference below the 10th centile for gestation. Most are constitutionally small and healthy. A minority are growth restricted from placental disease, infection, chromosomal abnormality or maternal factors. It matters because the growth restricted group has a higher risk of stillbirth, preterm birth, hypoxia in labour and neonatal hypoglycaemia.

• Risk factors: previous small baby, smoking, chronic hypertension, preeclampsia, malaria, undernutrition, anaemia, maternal age above 35 years or below 18 years, assisted conception.
• Most fetuses below the 10th centile are constitutionally small.
• The key task is to distinguish healthy small babies from growth restricted ones.

Women are usually asymptomatic. After 24 weeks the symphysis fundal height is 3 cm or more less than the weeks of gestation, or growth falters over 2 weeks, and some women report reduced fetal movements. Check blood pressure, weight gain, urine protein, liquor volume and fetal heart.

• Fundal height plotted below the 10th centile on a growth chart.
• Maternal weight gain below 0.5 kg per week in the third trimester.
• Differential diagnosis: wrong dates, constitutionally small fetus, placental insufficiency, congenital infection, chromosomal abnormality, oligohydramnios, ruptured membranes, fetal death.
• Complications: stillbirth, preterm birth, fetal hypoxia in labour, caesarean birth, neonatal hypoglycaemia and hypothermia, neonatal death.

The approach is to confirm dates, measure the fetus and look for a cause and for signs of placental dysfunction.

• Confirm dates with a first trimester crown rump length or the earliest scan.
• Ultrasound: estimated fetal weight, abdominal circumference, head to abdomen ratio, deepest vertical pocket (below 2 cm is oligohydramnios), umbilical artery and middle cerebral artery Doppler.
• Uterine artery Doppler at 20 to 24 weeks (mean pulsatility index above the 95th centile suggests placental disease).
• Maternal tests: blood pressure, urine protein, full blood count, malaria rapid test, syphilis test, HIV test, random glucose.
• Where ultrasound is unavailable, measure fundal height every 2 weeks from 24 weeks and refer when it lags by 3 cm or more.

The principle is to distinguish constitutional smallness from growth restriction, treat the cause and time delivery by Doppler findings.

• Supportive:
  • Stop smoking and alcohol.
  • Balanced protein and energy diet.
  • Daily fetal movement counts.
  • Avoid heavy work.
  • Treat anaemia.
• Pharmacological:
  • Malaria: artemether-lumefantrine 4 tablets (each 20 mg and 120 mg) oral at 0, 8, 24, 36, 48 and 60 hours.
  • Syphilis: benzathine benzylpenicillin 2.4 million units IM once weekly for 3 weeks.
  • Blood pressure 140/90 mmHg or more: 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).
  • Anaemia: ferrous sulphate 200 mg oral 8-hourly for 3 months.
  • Malaria prevention: sulfadoxine-pyrimethamine 3 tablets (500 mg and 25 mg each) oral monthly from 13 weeks.
  • Betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days if delivery within 7 days is likely.
  • Aspirin 150 mg oral at night from 12 weeks to 36 weeks in the next pregnancy.
• Procedures:
  • Induction of labour at 39 weeks for isolated small size with normal Dopplers, using misoprostol 25 micrograms vaginal 6-hourly (maximum 4 doses) or a Foley catheter with a 30 mL balloon.
  • Delivery at 37 weeks if growth restricted.
  • Continuous fetal heart monitoring in labour.
  • Caesarean section for abnormal Dopplers or obstetric indications.
• Special groups:
  • Women with HIV take co-trimoxazole 960 mg oral once daily instead of sulfadoxine-pyrimethamine.
  • Newborns feed within 30 minutes and have glucose checked within 2 hours, 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, deepest pocket below 2 cm, blood pressure 140/90 mmHg or more, vaginal bleeding, no growth over 2 weeks.
• Follow-up: growth scan with umbilical artery Doppler every 2 weeks; weekly Doppler if abnormal; paediatric review at birth; check weight and glucose of the newborn.