Is Your Baby Growing Too Slowly in the Womb? (Intrauterine Growth Restriction)

An expectant mother always tries to keep the baby in her womb healthy. But what should she do if the doctor or public health midwife who examines her says the baby is not growing well? Why does a baby's growth slow down? This article explains the situations in which a baby's growth in the womb is restricted.

How a baby's growth is checked

There are several ways to check a baby's growth. For a long time this was done by measuring the size of the mother's abdomen: the doctor uses a tape measure to check whether the abdomen is growing enough. This is a rough measurement, and it is not good at picking out babies who really are small. Where scanning is not available, however, it is still used as an alternative.

With today's scanning machines, the weight of the growing baby can be estimated quite closely. A special table or chart then shows whether that weight matches the number of weeks of pregnancy. Facilities to check by scan whether a baby is growing well are now available at almost every base hospital.

Why a baby may measure small

If a scan shows that a baby is smaller than expected for the stage of pregnancy, what could the reason be? There are a few main causes.

1. The due date is not correct. A pregnant mother's due date is calculated by counting 40 weeks from the first day of her last period. If that date is not remembered correctly, or if her periods are irregular, the due date can be wrong. In that case the due date is worked out from a scan done in the first three months of pregnancy.
2. The baby is naturally small. Not every baby grows to the same size. Just as adults differ in height and weight, babies growing in the womb differ from one another. Some babies are small but healthy, and they need no special treatment.
3. The baby is small because it is not getting enough nourishment. A baby receives food and oxygen from the mother through the placenta. If the placenta does not develop properly, the baby does not get enough nourishment, and its weight falls behind.
4. The baby has a medical condition. This is not common. Babies who have a medical condition are smaller than other babies. Genetic conditions or a serious infection in the mother can cause this. In such cases treatment depends on the condition.

Risk factors for having a small baby

1. The mother being over 40 years of age.
2. The mother developing a condition such as high blood pressure.
3. Smoking (the mother smoking, or being exposed to other people's smoke).
4. The mother being underweight (undernourished).
5. The mother exercising excessively.
6. High blood pressure, or a small baby, in a previous pregnancy.

Monitoring and delivery

The mother's abdomen is examined at every clinic visit. If the baby seems small, she is referred to a specialist, where a scan can show whether the baby is growing enough. Further tests are then recommended at the specialist clinic as needed. Usually the growth of these babies is measured by scan every two weeks. If any risk is found, early delivery is recommended; otherwise the pregnancy can continue under a specialist's supervision until the baby reaches a suitable size. Some babies also need Doppler and CTG tests from time to time.

Very small, high-risk babies need to be delivered by caesarean section, but many small babies can be born normally. Babies who are small because they were not well nourished in the womb catch up to a normal weight after birth. Breastfeeding them well is important.

Babies with a low birth weight have a higher risk of complications in the first few months, so they need to be looked after carefully. In adult life they are also more likely than babies of normal weight to develop conditions such as high blood pressure, diabetes and heart disease.