Macrosomia (Big Baby)

Reviewed by Edward Kulich, M.D.

Macrosomia is the term used to describe larger than average babies. Average newborns weigh around 7 pounds, 8 ounces, and newborns who weigh more than 9 pounds, 15 ounces are considered to be macrosomic. Health care providers may have a hard time determining if a baby is macrosomic while he or she is still in the womb. Generally, everyone must wait until the birth to determine how much a baby actually weighs. Still, doctors and experts look for signs and symptoms during the pregnancy to help them estimate fetal size. Ultrasounds are a tool used to get a more accurate idea of how big a baby is. Five to ten percent of newborn babies are considered macrosomic.

Macrosomia Causes

There are a variety of factors that can contribute to a large baby. While the most common factor is due to genetics, other causes and factors can be:

• High blood sugar levels from gestational diabetes or diabetes mellitus
• Ethnicity (Hispanic women are more at risk)
• Obesity
• Gaining extra weight during the pregnancy
• Carrying baby past term
• Gender (males are more susceptible)
• History of a previous large baby

It’s important to know that even if you are at risk from one or more of the factors above, you will likely still give birth to a normal sized baby. Often, big babies are born to mothers with none of the risk factors listed above. Unfortunately, the variation of birth weight remains unexplained, as many macrosomia babies have no identifiable risk factors.

Risks of a Macrosomia Baby

Fortunately, there are generally no significant problems associated with having a large baby. During delivery, macrosomia can occasionally lead to a broken collarbone (clavicle) for the baby.  The mother may suffer from excessive tearing in her perineum, and infections are always a concern if a tear occurs.

Macrosomia Treatment

In most cases there is no treatment needed for a baby with macrosomia. Problems that may occur for the mother include the ripping of the perineum at the time of delivery, the need to reduce blood sugar levels, and/or the need to reduce blood pressure levels. Lots of rest and relaxation are a great treatment, and infections that may occur are generally treated with antibiotics. Infants born to diabetic mothers are at risk for low blood sugar after birth.

If an ultrasound shows the baby has macrosomia, then your health care provider will more than likely schedule a c-section close to your due date. You may be monitored closely if your health care provider suspects macrosomia. However, it’s important to know that in most cases this is not a life-threatening condition for either mom or baby.