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.
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.
First steps in the management of a woman with a growth-retarded fetus consist of reversing any factors, such as smoking, drug use, or poor nutrition, that may be contributing to the problem. Sometimes the mother is admitted to the hospital for bed rest. Non-stress tests, contraction stress tests, or biophysical profiles are often done to check on the baby's condition. The expectant mother may be asked to keep a daily record of the baby's movements. Ultrasound exams are generally done every two weeks to track the baby's growth and the volume of amniotic fluid.
Amniocentesis might be performed to check for chromosome abnormalities or infection, two of the causes of IUGR. However, because it often takes about 10 days to obtain the results of amniocentesis, PUBS (percutaneous umbilical blood sampling) may be offered instead. In this procedure, ultrasound is used to guide a needle into the umbilical cord, and blood is withdrawn for analysis. Although the results are obtained more quickly with PUBS, there is a greater risk to the baby than with amniocentesis. Your doctor will discuss the pros and cons of these techniques with you if these tests are being considered.
If tests continue to show no evidence that the baby is in danger, and if the ultrasound exam shows that the baby is growing, the pregnancy may be continued until labor begins on its own. But signs that the fetus may be in danger or is not growing appropriately will prompt your doctor to consider early delivery. In weighing this decision, two questions are asked:
1. How mature is the baby?
2. How safe (or dangerous) is the uterine environment?
To answer the first question, amniocentesis may be performed to find out if the baby's lungs are fully mature. But some conditions may make it safer for the baby to be outside rather than inside the uterus, even if the baby is born early or the lungs are not mature. The expert care that can be given in a neonatal intensive care unit may be a better option for the baby than remaining inside the uterus under unfavorable conditions.
Depending on individual circumstances, birth may be accomplished by inducing labor and having the baby born vaginally or by cesarean. During labor, the baby will be monitored closely. If the fetal heart rate pattern or other tests indicate that the baby is not tolerating labor, a cesarean birth might be necessary. Whether a growth-retarded infant is born vaginally or by cesarean, there are still risks posed to the infant's health. You may be temporarily separated from your baby soon after birth so that she or he can be watched carefully for any complications, such as low blood sugar. A growth-retarded baby may need fluid with glucose (sugar) soon after birth. This may be given by bottle or through an intravenous line. The baby's temperature will also be monitored to make sure she or he remains warm enough.
Despite the many risks posed to the growth-retarded newborn, almost all of these babies go on to develop normally. The size of your baby at birth may not necessarily be an indication of how well she or he will grow and develop. Most growth-retarded babies tend to catch up with their normal counterparts by 18 to 24 months. Unless there are serious birth defects, the chances are good for most of these babies to have normal intellectual and physical development in the long term.
If you have had one growth-retarded baby, you are more likely to have another baby with this problem in a future pregnancy. Good prenatal care, excellent nutrition, and elimination of smoking and alcohol and drug use will increase your chances of having a healthy baby.