Macrosomic babies, or babies that are “large for gestational age,” have a birth weight of over 4,000 grams (8 lb 13 oz). Approximately nine percent of babies are born macrosomic. Macrosomia can lead to severe complications during pregnancy including shoulder dystocia and ensuing brachial plexus injuries, oxygen deprivation and brain damage, lacerations of the birth canal, uterine rupture, and urinary incontinence.
Babies born at weights over 4,500 grams (9 lb 15 oz) are at an even higher risk. Expectant mothers should be aware that certain risk factors make a baby more likely to be macrosomic, including the following:
- Obesity or significant weight gain during pregnancy. Obesity is one of the largest risk factors for macrosomia. Expectant mothers should follow nutritional guidelines and maintain a healthy weight throughout pregnancy.
- Maternal diabetes. Both pre-gestational diabetes and gestational diabetes (diabetes developed both before pregnancy and during pregnancy) are major risk factors for macrosomia. Increased blood sugar and insulin production lead to excessive growth, large shoulders, and fat deposits in a fetus. Expectant mothers with diabetes should discuss their situation with a doctor to manage diabetes during pregnancy. All expectant mothers should maintain good nutrition and a healthy weight to avoid developing gestational diabetes.
- Genetics. Babies with taller and larger parents are predisposed to be large themselves.
- Overdue pregnancy. Pregnancies that continue more than two weeks after the due date have increased risk of macrosomia.
- Previous pregnancies. Birth weight tends to increase somewhat in each of a woman’s pregnancy; thus, the incidence of macrosomia increases in babies whose mothers have given birth before. Prior delivery of a macrosomic baby increases the risk even more.
- Male baby. Male infants tend to weigh more than females. Most macrosomic babies are male.
- Maternal age. Women over 35 years of age are more likely to delivery a macrosomic baby.
- Ultrasound. An ultrasound can help a doctor to determine the size of a baby’s head, abdomen, and femur. These measurements can predict the baby’s weight with some degree of reliability.
- Height of the fundus. The fundal height, measured from the top of the pubic bone to the top of the uterus, usually corresponds with the length of the pregnancy. If the measurement of the fundus seems unusually large for the number of weeks of pregnancy, the baby may be larger than normal.