The term "fetal macrosomia" is used to describe a newborn who's significantly larger than average. A baby diagnosed with fetal macrosomia has a birth weight of more than 8 pounds, 13 ounces (4,000 grams), regardless of his or her gestational age. About 9 percent of babies born worldwide weigh more than 8 pounds, 13 ounces. However, the risks associated with fetal macrosomia increase greatly when birth weight is more than 9 pounds 15 ounces (4,500 grams). Fetal macrosomia may complicate vaginal delivery and could put the baby at risk of injury during birth. Fetal macrosomia also puts the baby at increased risk of health problems after birth.
Signs and symptoms
Fetal macrosomia is difficult to detect and diagnose during pregnancy. Possible signs and symptoms include:
• Large fundal height. During prenatal visits, your health care provider might measure your fundal height — the distance from the top of your uterus to your pubic bone. A fundal height that measures larger than expected could be a sign of fetal macrosomia.
• Excessive amniotic fluid (polyhydramnios). Too much amniotic fluid — the fluid that surrounds and protects a baby during pregnancy — might be a sign that your baby is larger than average. The amount of amniotic fluid reflects your baby's urine output, and a larger baby produces more urine. Some conditions that increase a baby's size might also increase his or her urine output.
If your health care provider suspects fetal macrosomia, a vaginal delivery isn't necessarily out of the question. However, you'll need to give birth in a hospital — in case forceps or a vacuum device are needed during delivery or a C-section becomes necessary. Inducing labor — stimulating uterine contractions before labor begins on its own — isn't generally recommended. Research suggests that labor induction doesn't reduce the risk of complications related to fetal macrosomia and might increase the need for a C-section. Your health care provider might recommend a C-section if:
• You have diabetes. If you had diabetes before pregnancy or you develop gestational diabetes and your health care provider estimates that your baby weighs 9 pounds, 15 ounces (4,500 grams) or more, a C-section might be the safest way to deliver your baby.
• Your baby weighs 11 pounds or more and you don't have a history of maternal diabetes. If you don't have pre-gestational or gestational diabetes and your health care provider estimates that your baby weighs 11 pounds (5,000 grams) or more, a C-section might be recommended.
• You delivered a baby whose shoulder got stuck behind your pelvic bone (shoulder dystocia). If you've delivered one baby with shoulder dystocia, you're at increased risk of the problem occurring again. A C-section might be recommended to avoid the risks associated with shoulder dystocia, such as a fractured collarbone.