Risk factors

Many factors might increase the risk of fetal macrosomia — some you can control, but others you can't.

For example:

• Maternal diabetes. Fetal macrosomia is more likely if you had diabetes before pregnancy (pre-gestational diabetes) or if you develop diabetes during pregnancy (gestational diabetes).

  If your diabetes isn't well controlled, your baby is likely to have larger shoulders and greater amounts of body fat than would a baby whose mother doesn't have diabetes.

• A history of fetal macrosomia. If you've previously given birth to a large baby, you're at increased risk of having another large baby. Also, if you weighed more than 8 pounds, 13 ounces at birth, you're more likely to have a large baby.
• Maternal obesity. Fetal macrosomia is more likely if you're obese.
• Excessive weight gain during pregnancy. Gaining too much weight during pregnancy increases the risk of fetal macrosomia.
• Previous pregnancies. The risk of fetal macrosomia increases with each pregnancy. Up to the fifth pregnancy, the average birth weight for each successive pregnancy typically increases by up to about 4 ounces (113 grams).
• Having a boy. Male infants typically weigh slightly more than female infants. Most babies who weigh more than 9 pounds, 15 ounces (4,500 grams) are male.
• Overdue pregnancy. If your pregnancy continues by more than two weeks past your due date, your baby is at increased risk of fetal macrosomia.
• Maternal age. Women older than 35 are more likely to have a baby diagnosed with fetal macrosomia.

Fetal macrosomia is more likely to be a result of maternal diabetes, obesity or weight gain during pregnancy than other causes. If these risk factors aren't present and fetal macrosomia is suspected, it's possible that your baby might have a rare medical condition that affects fetal growth.

If a rare medical condition is suspected, your health care provider might recommend prenatal diagnostic tests and perhaps a visit with a genetic counselor, depending on the test results.