Fetal Macrosomia

Fetal macrosomia is a condition in which the fetus is larger than average (between 4,000 grams [8 pounds, 13 ounces] and 4,500 grams [9 pounds, 15 ounces]). There are many causes, including diabetes or obesity in the birth parent. While fetal macrosomia is unpredictable, promoting good health and a healthy pregnancy can help prevent it.


What is fetal macrosomia?

Fetal macrosomia is a condition where your baby’s weight is in the top 10% of the stage of pregnancy you’re in. Delivering a large baby can be difficult, with more risk for vaginal tears or problems pushing your baby out. If your healthcare provider thinks that your baby is very big (more than 11 pounds, or more than 10 pounds if you have diabetes), a cesarean birth (C-section) may be the safest option.


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How is delivery affected if my baby is too big?

Having a large baby can increase your risk for certain complications during childbirth. Some of the most common include:

  • Injury to your birth canal, genital tract or perineum.
  • Heavy bleeding or postpartum hemorrhage.
  • Uterine rupture.
  • Longer labor, especially during the pushing phase.
  • Changes in your baby’s heart rate during labor.

Your baby is also at risk for complications. The most serious concern is shoulder dystocia. This happens when your baby's head emerges, but its shoulders get stuck inside of your uterus. This is a serious situation that can occur with any delivery, but it’s more common with large babies. Your healthcare provider will monitor your labor for signs of shoulder dystocia, as well as a plan of action should it happen.

In newborns, shoulder dystocia can cause:

Large newborn babies are also at risk for complications after delivery, including:

Symptoms and Causes

What are the symptoms of being pregnant with a big baby?

It’s hard to know the exact size of your baby until it’s born. Most of the pregnancy symptoms you experience are the same, regardless of your baby’s growth.


What causes fetal macrosomia?

Your healthcare provider may suspect your baby has macrosomia if you:

  • Have a large fundal height (a measurement of fetal growth).
  • Have gained a lot of weight during pregnancy.
  • Have diabetes, or were diagnosed with gestational diabetes.
  • You’ve previously delivered a large baby.
  • You’ve gone past your due date.
  • You were a big baby yourself.

Diagnosis and Tests

How is fetal macrosomia diagnosed?

Your healthcare provider may order an ultrasound to check the fetal weight and amount of amniotic fluid. An ultrasound is a diagnostic procedure that transmits high-frequency sound waves through body tissues. These waves transform into video or photographic images.

Ultrasound can only estimate a fetus's weight within about 10%. For instance, if the ultrasound estimates your baby is 9 pounds, that’s the “best guess.” But your baby could actually weigh somewhere between 8 pounds and 10 pounds.

As ultrasound isn’t precise and can’t predict shoulder dystocia, your healthcare provider will combine information from your ultrasound with your pregnancy history and physical exam to determine the safest timing and route of delivery.

To determine if you need an ultrasound exam, your healthcare provider will:

  • Measure your fundal height (the distance from the top of your uterus to your pubic bone).
  • Feel your belly. Your healthcare provider may press your abdomen in certain areas to judge the size of the fetus.

If your tests indicate the fetus is big, your prenatal care provider may suggest further testing to monitor fetal health. This could involve a biophysical profile or a nonstress test.


Management and Treatment

How is macrosomia treated when your baby is too big?

Treatment for macrosomia focuses on controlling any underlying health conditions you have like diabetes or obesity. You and your healthcare provider will work together to manage these and other conditions that may complicate your pregnancy or delivery. In most cases, implementing a healthy diet and exercise plan and controlling diabetes (with insulin, if needed) is all you can do.

Your healthcare provider will discuss the risks of a vaginal delivery with you. In some cases, a C-section is recommended to reduce the chances of a complication. It’s important to know that delivering your baby early doesn’t seem to reduce complications, so scheduling a delivery prior to 39 weeks isn’t recommended unless there are other medical complications besides your baby’s size.

Do I need a C-section if my baby is too big?

Not necessarily. A C-section is more likely to occur when:

  • You’ve had a baby with shoulder dystocia.
  • You have diabetes, and your baby is estimated to be over 10 pounds.
  • You don’t have diabetes, and your baby is predicted to weigh more than 11 pounds.


Can fetal macrosomia be prevented?

Fetal macrosomia is often unpredictable. The diagnosis is made only after your baby has been weighed after delivery. Babies can be born larger than average with or without any known risk factors.

Promoting good health and a healthy pregnancy can improve the odds:

  • Get regular prenatal care. Frequent visits allow you and your healthcare provider to closely follow your baby’s progress and also give you a chance to ask questions.
  • Watch your weight. Your weight before pregnancy matters, as does how much weight you gain while you’re pregnant.
  • If you have diabetes, take appropriate steps to manage it. Diabetes before your pregnancy and diabetes that happens during your pregnancy (gestational diabetes) are risk factors for fetal macrosomia.

Outlook / Prognosis

What are the complications of fetal macrosomia to the baby?

Research suggests that large babies are at greater risk of:

  • Having low blood sugar (hypoglycemia).
  • Having obesity in childhood.
  • Developing metabolic syndrome (a cluster of conditions that increase the likelihood of heart disease, stroke and diabetes).

Most babies who suffer fractures or nerve damage during delivery recover fully from those injuries.

A note from Cleveland Clinic

Fetal macrosomia can cause serious complications during childbirth. There are many causes, but the two most important are uncontrolled diabetes and having obesity. You can reduce your risk of having a large baby by managing these conditions. Regular exercise and eating a healthy diet can help you achieve a healthy pregnancy and reduce your risk of complications. Don’t be afraid to ask questions about how you can take care of yourself. While fetal macrosomia can be serious, most macrosomic babies are born healthy.

Medically Reviewed

Last reviewed on 05/13/2022.

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