Fetal growth restriction: Causes, complications, and tests to be done

By Dr. Vanisree Padige

The evaluation of fetal growth is one of the key objectives of prenatal care. Identification of a small fetus, classifying fetal growth restriction, understanding the etiology and risk factors, formulating a comprehensive strategy, and timing of delivery is imperative to have a successful perinatal outcome.

What is meant by a small baby during pregnancy?

There are two entities in this, one is small for gestational age fetus and the other is fetal growth restriction. Small for gestational age fetus is defined when the size of the fetus falls below a predefined threshold for that stage of pregnancy, commonly taken as estimated fetal weight or abdominal circumference below 10th percentile.

It means SGA fetus may be small but not at increased risk of adverse perinatal outcome. Whereas fetal growth restriction is defined as the failure of the fetus to meet its biological growth potential due to pathological factors.

What could be the causes?

The baby’s weight is affected by many factors, including parental height and weight, ethnicity, gender of the baby, etc. In the above cases, if the baby is small, the baby is likely to be healthy because he or she is meant to be small.

However, growth restricted babies are small because of one or more maternal / placental or fetal disorders that interfere with the normal mechanism of fetal growth. These could be:

a. The placenta not working as well as it should. This could be because of medical problems such as high blood pressure or its complications, smoking, recreational drugs, or being very anaemic.

b. An infection during pregnancy that affects the baby (such as cytomegalovirus, toxoplasmosis, zika virus, malaria)

c. Having a baby with a developmental or genetic problem

What increases the risk of having growth restricted babies?

Lifestyle choices such as smoking, using cocaine, over exercising or not eating healthily are all linked to an increased chance of the baby being growth restricted. Other factors that increase this risk are advanced maternal age (>40 years), high blood pressure, kidney problems or diabetic complications, autoimmune conditions, anaemia, etc.

How to reduce the risk?

Some of the risks cannot be changed, but some can. Lifestyle modifications should ideally be done before conception.

• • Reducing or quitting smoking
• • Not using recreational drugs
• • Leading a healthy lifestyle and eating healthy
• • Medical interventions – low dose aspirin is recommended for women at increased risk of pre eclampsia.

What are the complications of fetal growth restriction?

If the baby is growth restricted, there is increased risk of still birth (the baby dying in the womb), serious illness and dying shortly after birth. The earlier in the pregnancy and more severe the growth restriction, poorer is the outcome for the baby.

How to identify growth restricted babies?

1. Screening for high risk factors can be done before pregnancy, at booking in the antenatal clinic and at every antenatal visit.

2. If the woman is low risk, baby growth can be monitored at each antenatal appointment from 24 weeks of pregnancy by symphysis fundal height (the distance between the pubic bone and the top of the womb) measurement and plotted on a chart. If growth slows down, then ultrasound scan is advised.

3. If the woman is at increased risk of having small baby/fetal growth restriction, then it is recommended to have:

• • regular ultrasound scans from 26-28 weeks of pregnancy onwards
• • also, ultrasound scan of the blood flow to the placenta (i.e., uterine artery doppler test) is done at 20-24 weeks of pregnancy. Depending on the results, further scans can be advised.

What other tests are to be done if the baby is small or not growing?

• • Umbilical artery doppler: This measures the flow of blood through the umbilical cord.
• • Cardiotocograph: Tracks the baby’s heart rate.
• • Measuring the amount of amniotic fluid around the baby.
• • Referral to a fetal medicine specialist for more frequent and detailed scans if umbilical artery doppler test is abnormal.

Timing of delivery

This will depend on how severely the fetus growth is affected and on the doppler measurements. The scan will help the obstetrician decide whether it is better to deliver the baby early or safer for the pregnancy to continue.

- If the baby is growing and the doppler tests are normal, it is best to wait until pregnancy is at least 37 weeks with more frequent monitoring of the baby.

- If the doppler tests are abnormal and pregnancy is less than 34 weeks, a course of corticosteroids is given before delivery. This is to help the baby’s development and reduce the chance of breathing problems after birth.

Mode of delivery

If there are no other complications, vaginal birth can be aimed in growth restricted fetuses with normal doppler test. However, if the umbilical artery doppler tests are abnormal, it is recommended that the baby be delivered by caesarean section.

Place of birth (where should these babies be born)

It is advised to have fetal growth restricted babies delivered in a hospital where there is a neonatal unit/special care baby unit because these babies are at increased risk of complications, they require closer follow-up than normally grown infants in the first year of life.

Advise for future pregnancies

• • Optimise chronic medical conditions like hypertension, anaemia, diabetes and other medical diseases
• • Manage as high risk pregnancy
• • Stratify the risk in early pregnancy with screening tests
• • Closer antenatal surveillance, including close monitoring of fetal growth and maternal blood pressure

Dr. Vanisree Padige
Consultant Obstetrician and Fetal Medicine Specialist D.G.O, MRCOG
Rainbow Children's Hospital, Kondapur, Hyderabad.

This article was published in association with Rainbow Children’s Hospital.