Fetal growth abnormality is an umbrella term that refers to any abnormality in how a baby grows inside the womb. According to the Nemours Foundation, newborns typically weigh between 6 lbs., 2 oz. and 9 lbs., 2 oz. and can range from 19 to 21 inches in length. Newborns that are significantly larger or smaller than normal are considered to have a fetal growth abnormality. While many pregnancies with fetal growth abnormalities will be born at term–37 weeks after conception–other will be born before the 37 weeks mark and thus be premature.
There are generally two main types of fetal growth abnormalities: intrauterine growth restriction (IUGR) and macrosomia. Babies affected with IUGR, which is also known as fetal growth restriction, are considered small for gestational age. Babies suffering from macrosomia, on the other hand, are considered large for gestational age. Macrosomia is also known as big baby syndrome.
Because of the way most fetal growth abnormalities are defined, around 20 percent of all births will be associated with fetal growth problems. IUGR is generally defined as a fetal weight that falls below 90 percent of the fetuses in the same gestational age. Conversely, newborns affected with macrosomia weigh more than 90 percent of the newborns in the same gestational age, which is typically between 8 lbs., 13 oz. to 9 lbs., 15 oz. or more.
The most common cause of IUGR is an abnormality in the placenta that prevents the fetus from receiving the proper amount of oxygen and nutrients. A number of other factors can increase the risk of IUGR, including maternal factors such as cigarette smoking, high blood pressure and alcohol or drug abuse. According to the American Academy of Family Physicians, diabetes in the mother doubles the risk of fetal macrosomia and is the most common cause of the abnormality. Genetics can also contribute to macrosomia, as well as excessive maternal weight gain before or during the pregnancy.
Prevention and Treatment
IUGR can occur in mothers of good health, but a nutritious diet and avoiding harmful factors such as cigarette smoking and drug use can lower the risks. Treatment for IUGR can include increasing the amount of nutrition for the mother, mandatory bed rest to increase circulation and, if the health of the fetus is in danger, a doctor may recommend an induced labor to deliver the baby early. Pregnant women may be able to lower their risk of fetal macrosomia by avoiding excessive weight gain, and treatment may include a cesarean section.
Besides being smaller, babies affected with IUGR have an increased risk of being stillborn, may have a lower resistance to infection and may appear pale and thin with loose, dry skin and a wide-eyed look. While many IUGR babies will grow to normal size within a couple years, others may have long-term growth problems. Fetal macrosomia is also associated with a risk of stillbirth. Also, if the baby is delivered vaginally, there is an increased risk of trauma during birth for the newborn such as shoulder dystocia.