My Baby Is Very Large! Could He Have Fetal Macrosomia?

Fetal Macrosomia

You probably know about the various health risks associated with low birth weight but did you know that big babies can also have their own health issues?

What is fetal macrosomia?

‘Fetal macrosomia’ is the term used to describe a newborn who is significantly larger than average. For a baby to be diagnosed with fetal macrosomia, their birth weight should higher than 8 pounds 13 ounces (4000 grams). Globally, approximately 9 percent of babies are born in this category. The health risks associated with fetal macrosomia increase substantially when the newborn baby has a weight of more than 9 pounds 15 ounces (4500 grams). 1

Following are some potential health risks to the mother from having a baby with fetal macrosomia:

  • Uterine rupture – if you had a previous C-section or other major uterine surgery, fetal macrosomia can result in uterine rupture; however, this is a rare event.
  • Labor problems – A larger than usual baby can become stuck in the birth canal, is more likely to experience shoulder dystocia, or is more likely to need forceps or a vacuum device during delivery.2
  • Genital tract lacerations – When the newborn has fetal macrosomia, the mother is more likely to have tearing of vaginal tissue as well as of the muscles between the vagina and the anus.
  • Bleeding after delivery – The risk of potentially serious bleeding caused by your uterine muscles not contracting properly after birth is increased with fetal macrosomia.1

In addition to complicating a vaginal delivery and putting the baby at risk of injury during birth, there is a higher concern of health problems after the birth. These include the baby being born with lower than normal blood sugar level, a higher risk of obesity in childhood, and a higher risk of developing metabolic syndrome (a condition characterized by increased blood pressure, excess body fat around the waist, high blood sugar level or abnormal cholesterol levels) during childhood.

What causes fetal macrosomia?

Fetal macrosomia can be caused by genetic factors or by maternal conditions such as obesity or diabetes. It can also be caused by:

  • Excessive weight gain during pregnancy
  • A pregnancy that goes two weeks past the due date
  • A maternal age of more than 35 years
  • The gender of the baby – boys are more likely than girls to weigh more than 9 pounds 15 ounces (4500 grams) at birth.1

How can I tell if my baby has fetal macrosomia?

Unfortunately, fetal macrosomia is difficult to detect during pregnancy.

Possible signs and symptoms include:

  • Excessive amniotic fluid (also called polyhydramnios): If there is a lot of amniotic fluid surrounding your baby, this might be a sign that he is larger than average. The amount of amniotic fluid reflects your baby’s urine output and a larger baby tends to produce more urine.
  • Large fundal height: Your fundal height is the distance from the top of your uterus to your pubic bone. If this distance is larger than normal, it could be a sign that your baby has fetal macrosomia. However, results from fundal height measurements aren’t always reliable.1

How can I help my baby avoid being diagnosed with fetal macrosomia?

If you are overweight before getting pregnant, consider undergoing a weight loss program before pregnancy. If you have a normal body weight at the start of pregnancy, try to avoid excessive weight gain during pregnancy.3 If you have risk factors such as diabetes or obesity during the pregnancy, close monitoring is recommended and possibly a C-section or induction may be suggested.4

References:

  1. Fetal Macrosomia
  2. Contemporary Management of Shoulder Dystocia
  3. How to avoid an abnormally large baby
  4. Management of Suspected Fetal Macrosomia
Melody Watson

Melody Watson holds Bachelors degrees in Biochemistry and Microbiology. She works as a medical writer for a medical communications agency in Berlin, Germany, where her work ranges from medical translation to writing publications for medical journals. Melody is passionate about promoting science, including evidence-based medicine, and debunking pseudoscience.


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