Mothers who are obese during pregnancy are more likely to give birth to an atypically large infant, a new U.S. study suggested Monday.
The findings, published in the U.S. journal JAMA Pediatrics, were based on an analysis of more than 2,800 pregnant women, including 443 obese women with no accompanying health conditions, such as diabetes, and more than 2300 non-obese women.
Ultrasound scans taken during pregnancy revealed that for fetuses of obese women, the femur, or thigh bone, and humerus, or upper arm bone, were longer than those of the fetuses of non-obese women starting in the 21st week of pregnancy.
For fetuses in the obese group, the average femur length was 0.8 millimeters longer, compared to the non-obese group, and humerus length was about 1.1 millimeters longer, compared to the non-obese group.
Average birth weight was about 100 grams heavier in the obese group.
Previous studies showed that macrosomia -- large body size at birth -- increases not only the risk that an infant will experience bone fracture during delivery, but also the likelihood that the infant will need to be delivered by cesarean section.
Meanwhile, having a large infant also increases a mother's risk for postpartum hemorrhage, or excessive bleeding at birth.
"Our results underscore the importance of attaining a healthy body weight before pregnancy," said the study's lead author, Cuilin Zhang, a researcher at the U.S. National Institutes of Health.
"They also suggest that clinicians should carefully monitor the pregnancies of all obese women, regardless of whether or not they have obesity-related health conditions."
The study could not determine exactly why the fetuses of obese women were larger and heavier than fetuses in the non-obese group.
The researchers theorized that because obese women are more likely to have difficulty using insulin to lower blood sugar, higher blood sugar levels could have promoted overgrowth in their fetuses.
The authors also pointed out that earlier studies have indicated that the higher risk of overgrowth seen in newborns of obese women may predispose these infants to obesity and cardiovascular disease later in life.
They called for additional studies to follow the children born to obese women to determine what health issues they may face.