Obesity During Pregnancy Raises Birth Defect Risk

Jun 12, 2004 12:28 PM EDT

According to recent research women who are obese during pregnancy put their babies at greater risk for birth defects.

Researchers examined data from births in a five-county area of metropolitan Atlanta between January 1993 and August 1997. The scientists studied 645 infants with birth defects and 330 without in a case-controlled study. The study’s findings were published in the journal, Pediatrics.

Mothers were considered overweight if they had a body-mass index between 25 and 30, and obese if the index—a height-weight ratio—was 30 or higher.

Up to 20% higher risk

Compared with women who were of healthier weight in the study, those who were obese or overweight before pregnancy faced double the risk of having babies with heart defects and double the risk of multiple birth defects. Normally, 3 to 5% of infants are born with major birth defects. Obese women faced an even higher risk—more than triple that of normal-sized women—of having babies with a defect known as omphalocele, in which intestines or other abdominal organs protrude through the navel.

The researchers said their study also confirmed an already reported link between pre-pregnancy obesity and neural tube birth defects, including spina bifida.

Reasons are uncertain

Reasons for the links are uncertain, but may include nutritional deficits in women with poor eating habits or diabetes, which is common in obesity and is known to increase risks for birth defects. It may also be that obese women have increased but sometimes unmet needs for nutrients that can protect against some birth defects, such as folic acid.

Statistics have shown that more than half of US women 20 to 34 years old are overweight, with 25% of those classified as obese.

An average woman should gain 25 to 35 pounds during pregnancy, but overweight women should gain only 15 to 25 pounds and obese women less than 15 pounds.


1. S. M. Mone; et al., “Effects of Environmental Exposures on the Cardiovascular System: Prenatal Period through Adolescence,” Pediatrics, 2004; 113: 1058 - 1069.