Fetal Macrosomia

Fetal macrosomia occurs when the infant is unusually large for his or her gestational age. It can cause birth injuries and complications.

During pregnancy, physicians must carefully monitor both infant and mother to ensure that the pregnancy is developing normally. They must also diagnose and treat any issues that can result in potential birth injuries. One possible complication is fetal macrosomia, a condition in which babies are unusually large for their gestational age. Macrosomia can lead to a host of medical issues, including birth injuries and life-threatening medical complications.

What is Fetal Macrosomia?

When an infant’s estimated weight is higher than 90 percent of the average weight of babies in the same age range, they are considered large for their gestational age. Yet that’s only part of how fetal macrosomia is defined. Macrosomia is also considered a high-risk pregnancy in which the mother and infant are at risk for medical problems.

Most doctors consider macrosomia to be a birth weight of more than 9 pounds, 15 ounces. Some doctors consider it to be a birth weight of more than 8 pounds, 13 ounces.

fetal macrosomia

It makes normal delivery extremely difficult, often ending in a cesarean section surgery (C-section) and/or early labor induction.

Fetal Macrosomia Symptoms

Unfortunately, fetal macrosomia is often difficult to detect during pregnancy. There there a few tests that can be performed if there are signs of an unusually large baby. Doctors will check for signs, including:

  • Excessive Amniotic Fluid: During a prenatal visit, a physician can measure amniotic fluid via an ultrasound. Excessive amounts of amniotic fluid may indicate that the infant is larger than the expected size. Larger babies tend to urinate more, which leads to a higher amount of amniotic fluid.
  • Fundal Height: During a prenatal visit, physicians can also measure the distance of a pregnant woman’s pelvic bone to her uterus. Known as a fundal height measurement, this gives doctors a better understanding of how large the infant is.
  • Ultrasound: Measurements of the estimated fetal weight by ultrasound is the primary method to diagnose macrosomia despite an error rate or variance of 15 percent.

What Causes Fetal Macrosomia?

According to Carol L. Archie, M.D.  of the University of California at Los Angeles School of Medicine, maternal diabetes and obesity can lead to macrosomia as an infant typically receives too many nutrients.

“Big parents often have big babies, but sometimes babies are unusually large because the mother is obese or has developed gestational diabetes during her pregnancy that was undiagnosed or untreated,” Dr. Archie says.

Untreated gestational diabetes is a very possible cause of large infants. Other factors that have been associated with fetal macrosomia include post-term pregnancies, mothers of Hispanic origin and a history of previous large infants. Male infants also have a higher rate of being born with macrosomia when compared to female infants.  In addition, women over the age of 35 have a higher risk of having large babies.

In some cases, there is no known cause of fetal macrosomia.

Fetal Macrosomia Complications

Both mother and infant are at risk for complications. For mothers, one of the major complications includes a difficult pregnancy. If a normal labor and delivery occurs, a large infant may become caught in the birth canal. This can result in doctors using birth-assisting tools to help delivery. This may cause genital tract lacerations, excessive bleeding and the need for an emergency C-section.

Infants are at heightened risk for birth injuries. For instance, a difficult labor and delivery process puts a baby in danger of shoulder dystocia, nerve damage and oxygen deprivation at birth if there is shoulder dystocia. Any of these can lead to permanent health issues and disorders. If oxygen and blood flow both are restricted, then then your baby may have what is called a hypoxic ischemic brain injury.

Furthermore, infants with a high birth weight may have childhood obesity and are at risk of developing metabolic syndrome. Metabolic syndrome is a condition marked by high blood sugar levels, increased blood pressure and excessive body fat around the waist and abdominal area. When these issues are combined, the child is also in danger of heart disease and stroke later on in life.

Fetal Macrosomia Treatment Options

If fetal macrosomia is caused by gestational diabetes, physicians will work closely to ensure the mother regulates her blood sugar . This can include following a healthy diet plan and a safe exercise regimen. It may include medications such as insulin if blood sugars are consistently high.

Although having a normal delivery is not necessarily impossible for mothers with large infants, a C-section, in many cases, is the best option. Although a C-section comes with its own set of risks and complications, the benefits typically outweigh the hazards. For example, a C-section will eliminate the possibility of birth injuries caused by birth-assisting tools as well as injuries such as shoulder dystocia and a fractured collarbone.

Fetal Macrosomia Prevention

Even though there are some cases in which fetal macrosomia occurs for no apparent reason, pregnant women can help reduce the chances by:

  • Watching Weight Gain: Although this may be difficult during pregnancy, gaining between 25 to 35 pounds only, the ideal weight gain during pregnancy, is recommended by most doctors. It’s important to note, however, that this is just a general guideline, and doesn’t apply to each individual case. A physician should work closely with you in order to find the ideal weight gain amount for your situation.
  • Control Diabetes: Controlling blood sugar during pregnancy is one of the best ways to help prevent fetal macrosomia.
  • Keep All Prenatal Appointments: Prenatal check-ups are crucial during pregnancy as it allows doctors to examine the pregnancy and run tests to ensure everything is normal. It also helps them prepare for your upcoming birth and the steps needed should you show signs of carrying a large infant.

Kimberly Langdon

Page Medically Reviewed By Kim Langdon, M.D.

Kimberly Langdon, M.D. is a retired board-certified OB/GYN with 19 years of clinical experience. She currently works as a medical writer and featured healthcare expert. She is a regular medical reviewer for Birth Injury Guide.

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