Women who are obese when they become pregnant appear to be more likely to give birth to babies with various birth defects than women of healthy weight, new research suggests.
Moreover, simply being overweight but not obese at the time of conception seems to increase the risk of having a child with heart defects or more than one unrelated birth defect.
Previous research showed that women who are obese before becoming pregnant have a higher-than-average risk of giving birth to a baby with defects in the brain and spinal cord, and the current findings extend that risk to other types of defects.
During the current study, researchers at the Centers for Disease Control and Prevention in Atlanta, Georgia, interviewed mothers of more than 600 babies born with certain birth defects between 1993 and 1997 and compared their responses to those of 330 mothers of babies who did not have those birth defects.
The researchers determined whether a woman carried excess body weight before giving birth by asking her height and weight before she became pregnant, then using that information to calculate her body mass index (BMI).
The authors found that women who were obese before pregnancy were more than three times as likely as women of average weight to have children with spina bifida, a defect in which one or more of the vertebrae fails to develop completely, leaving a portion of the spine exposed.
Obese women were also twice as likely to have a child with heart defects and more than three times as likely to give birth to a baby with a defect in the abdominal wall known as omphalocele.
Relative to women of healthy weight, women who were overweight but not obese had around a two-fold higher risk of having infants with either heart defects or more than one unrelated birth defect.
The reasons why excess weight in the mother can increase the risk of birth defects is unclear. It is possible that overweight and obese women may have certain metabolic abnormalities that could affect the growth of cells in a developing embryo. Alternatively, overweight and obese mothers may have undiagnosed diabetes, a condition that has been shown to increase the risk of birth defects.
The researchers say that it may be a good idea to get the message out early to women -- even before they are ready to conceive -- that their weight can place their unborn child at risk.
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