Symmetrical Fetal Growth Restriction

Symmetrical fetal growth restriction is a fetus with head, abdomen and femur all proportionately small, below the 10th centile, with a normal head to abdomen ratio. It reflects an insult from early pregnancy such as chromosomal abnormality, congenital infection, drug exposure or severe undernutrition. It matters because the cause is often not treatable, the outlook is poorer than for late placental growth restriction, and counselling is needed.

• A minority of growth restriction is symmetrical.
• Risk factors: maternal age above 35 years, alcohol, smoking, malaria, syphilis, HIV, cytomegalovirus, toxoplasmosis, malnutrition.
• Check dates first, because wrong dates mimic it.

Women are usually asymptomatic, with fundal height more than 3 cm smaller than dates from the second trimester. Some report reduced fetal movements or have a history of fever, rash or exposure.

• Small fundal height from 20 weeks.
• Possible anomalies on scan.
• Differential diagnosis: wrong dates, constitutionally small fetus, placental insufficiency (asymmetrical growth restriction), trisomy 18, trisomy 13, triploidy, congenital infection, fetal alcohol exposure.
• Complications: stillbirth, preterm birth, neonatal death, congenital anomaly, long term neurological impairment, hearing loss from infection.

The approach is to confirm dates, find anomalies and test for infection and chromosomal disease.

• Ultrasound: head circumference, abdominal circumference and femur length all below the 10th centile, head to abdomen ratio normal; detailed anomaly scan and fetal heart scan.
• Umbilical artery Doppler is usually normal early on.
• Maternal tests: syphilis, HIV, malaria rapid test, cytomegalovirus, toxoplasma and rubella IgM and IgG; hepatitis B.
• Amniocentesis for quantitative fluorescent PCR or microarray and cytomegalovirus PCR where available.

The principle is to treat infection where possible, counsel on prognosis and plan birth by gestation and Doppler findings.

• Supportive: stop alcohol and smoking; nutrition; daily fetal movement counts; counselling on the outlook, including plans for care of a baby with poor prognosis.
• Pharmacological: benzathine benzylpenicillin 2.4 million units IM once weekly for 3 weeks for syphilis; artemether-lumefantrine 4 tablets (each 20 mg and 120 mg) oral at 0, 8, 24, 36, 48 and 60 hours for malaria; tenofovir 300 mg, lamivudine 300 mg and dolutegravir 50 mg oral once daily for HIV; spiramycin 1 g oral 8-hourly until delivery for toxoplasma infection with a normal fetus; valaciclovir 2 g oral 6-hourly for confirmed fetal cytomegalovirus infection with normal kidney function; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days if delivery 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.
• Procedures: amniocentesis for karyotype; delivery at 37 weeks if Dopplers are normal and earlier for abnormal Doppler or cardiotocography; intervention for fetal compromise only after counselling in chromosomal disease with poor prognosis.
• Special groups: chromosomal abnormalities with lethal prognosis, such as trisomy 13 and 18, need counselling about avoiding operative birth for fetal indications and planning of palliative neonatal care.
• Red flags: reduced fetal movements, absent or reversed end diastolic flow, oligohydramnios, hydrops, maternal fever with rash.
• Follow-up: growth scan every 2 weeks; Doppler weekly; paediatric review at birth with hearing, eye and head ultrasound tests; genetic counselling for the next pregnancy.