Birth Definitions

Macrosomia Definition


Macrosomia is a medical term used to describe an unusually large baby. It is generally defined as a birth weight of more than 8 pounds 13 ounces (4,000 grams). The average birth weight in the United States is about 7 pounds 3 ounces (3,300 grams).

There are several factors that can contribute to macrosomia, including gestational diabetes, maternal obesity, advanced maternal age, and certain medications. Additionally, certain ethnic groups are more likely to have babies with macrosomia, such as Hispanic and Native American women.

While macrosomia itself is not necessarily dangerous, it can increase the risk of complications during labor and delivery. These complications include shoulder dystocia (when the baby’s shoulder gets stuck behind the mother’s pubic bone) which can result in nerve damage or even death, birth trauma, and cesarean delivery. Babies who have macrosomia are also more likely to develop obesity and type 2 diabetes later in life.

Macrosomia should not be confused with gigantomastia, which is a rare condition characterized by excessive growth of the breasts during pregnancy.

If you are pregnant and have any concerns, be sure to discuss them with your healthcare provider.

Some terms that are closely associated with macrosomia include:

  • Birth weight
  • Gestational diabetes
  • Obesity
  • Shoulder dystocia
  • Medications (e.g., corticosteroids, anticonvulsants)
  • Delivery complications
  • Large for gestational age (LGA)
  • Heavy for dates” (HFD)

This image shows how often the term ‘Macrosomia’ is used in relation to other, similar birth terms:

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