Intrauterine Growth Retardation

What causes Intrauterine Growth Retardation and who's at risk?

Each year in the United States, as many as 40,000 babies are born at term with a birth weight of less than 2,500 grams (less than 5 1/2 pounds). Because of less-than-optimal conditions inside the uterus, these babies did not grow as rapidly as they should have during pregnancy, a problem known as intrauterine growth retardation (IUGR).

Advances in medicine have greatly reduced the risks for growth-retarded infants, but they are still at risk for numerous problems. These babies have low stores of body fat and glycogen (a type of carbohydrate that is readily transformed into glucose, an energy source). As a consequence, they are unable to conserve heat and may develop hypothermia. Stillbirth and fetal distress are also more common in growth-retarded fetuses. Because of their lower energy stores, these fetuses are less able to tolerate the stress of labor than an infant of normal size.

Possible causes of IUGR include problems with the placenta that prevent it from delivering enough oxygen and nutrients to the fetus. This may occur as the result of high blood pressure in the mother, but it can also occur without a known cause. Other causes of IUGR include the following:

• Cigarette smoking
• Certain infections (such as rubella, cytomegalovirus, or toxoplasmosis)
• Birth defects or chromosome abnormalities
• Severe malnutrition
• Drug or alcohol use
• Juvenile diabetes
• Rheumatologic diseases
• Other chronic diseases in the mother

Women who have had a growth-retarded infant in a previous pregnancy are at an increased risk to have another undersized baby. Fortunately, careful monitoring and early intervention often can help lessen some of the dangers posed to growth-retarded infants. In some cases, growth retardation can even be reversed.

How is Intrauterine Growth Retardation diagnosed?

A woman carrying a growth-retarded fetus usually has few, if any, symptoms to alert her to the problem. The careful measurements your doctor makes at each of your prenatal visits are partly intended to detect IUGR at an early stage.

This is one reason your doctor measures the fundal height of your uterus — the distance between your pubic bone and the fundus, or top, of your uterus. Between 18 and 34 weeks, this measurement in centimeters corresponds roughly to the number of weeks of pregnancy. By looking at how this measurement increases over time, the doctor may be alerted to IUGR if the size of the uterus does not seem to be increasing as it should.

Accurate dating of your pregnancy is important for making the diagnosis of IUGR. If this date is off by even one or two weeks, it may be impossible to diagnose the condition correctly. Before about 20 weeks of pregnancy, an ultrasound exam can be used to determine the gestational age as precisely as possible.

If IUGR is suspected because of low fundal height measurements, an ultrasound exam likely will be done to confirm the diagnosis. This test can be used to measure some of the physical features of the fetus. The circumference of the head and abdomen, and the ratio of one to the other, is one of the most useful of these measurements. Other measurements that may be taken include the width of the baby's head (called the biparietal diameter, or the distance between the two side bones of the skull), the length of the thigh bone (femur), and the amount of amniotic fluid.