Fetal Growth Restriction During Pregnancy: Causes, Diagnosis & Care

In short: Fetal growth restriction means the baby does not reach the size expected from its genetic potential. The main causes are a poorly working placenta, long-term illness in the mother such as high blood pressure and diabetes, and chromosome abnormalities. It is diagnosed by ultrasound and followed by measuring the amniotic fluid, Doppler blood flow and the baby’s heart trace. Delivery is aimed for at week 37 if possible, often by caesarean.

Every expectant parent hopes for a smoothly growing baby, so hearing that your fetus is smaller than expected can feel worrying. Understanding what fetal growth restriction means — and how it is carefully monitored — can help ease that concern.

What is fetal growth restriction during pregnancy?

Fetal growth restriction happens when the fetus does not reach the size that matches its genetic potential.

It is worth noting that some fetuses are simply small because of their genetic makeup — for example, when the mother or father are naturally small in size and build. This is not the same as true growth restriction.

What are the causes of fetal growth restriction during pregnancy?

• Placental dysfunction
• Chronic maternal conditions such as high blood pressure, pre-eclampsia, kidney disease, diabetes, and thyroid problems - Smoking, alcohol or drug use - Infections in the baby such as cytomegalovirus (CMV) or toxoplasmosis
• Chromosomal problems
• Genetic problems

Women at high risk (for example, a previous baby with growth restriction, high blood pressure or kidney disease) are usually advised to take low-dose aspirin every night from about 12 weeks until 36 weeks, and stopping smoking greatly lowers the risk.

How do we diagnose fetal growth restriction during pregnancy?

• Small abdominal size compared to the calculated gestational age
• Fetal measurements on ultrasound are small compared to the calculated gestational age: an estimated weight or abdominal size below the 10th centile, especially below the 3rd centile or with abnormal Doppler blood-flow results, or growth that slows down on serial scans

How are pregnancies in which the fetus suffers from growth restriction managed?

Close monitoring is key to caring for both mother and baby. This typically includes:

• Ultrasound monitoring of the fetus (amniotic fluid, fetal blood flow, placental appearance, fetal brain blood flow)

• A detailed anomaly scan by a fetal medicine specialist to check the baby’s anatomy

• Chromosomal/genetic testing if a defect is suspected

• [If early delivery is expected before about 35 weeks, steroid injections are given to mature the baby’s lungs (and magnesium sulphate to protect the brain if delivery is before about 32 weeks)

• Periodic fetal heart rate monitoring through CTG

When is a fetus with intrauterine growth restriction delivered?

This depends on the follow-up results. Sometimes, we may have to deliver the baby early, but we try as much as possible to reach the 37th week of pregnancy.

How is a fetus with intrauterine growth restriction delivered?

This depends on the baby’s condition. If the Doppler blood-flow tests or the fetal heart tracing show that the baby is under significant stress, a cesarean section is safer. Otherwise, a vaginal birth (often by induction of labor) is possible, with continuous monitoring of the baby’s heartbeat during labor and a low threshold for cesarean if problems arise.

If you have concerns about your baby’s growth during pregnancy, Dr. Najeeb Layyous and his team offer careful ultrasound monitoring and personalized follow-up care to help guide you through every stage of your pregnancy.

These injections are explained in our article on steroids for fetal lung maturity.

Dr Najeeb Layyous F.R.C.O.G

Consultant Obstetrician, Gynecologist and Infertility Specialist