According to a study supported by the National Institutes of Health (NIH), women who are obese at the time they become pregnant increase their chances of having a baby with a congenital heart defect, in some instances by as much as 33%. The risk increases with the mother’s level obesity, with women who were morbidly obese having a 33% chance, and mothers who were moderately obese having an 11% higher likelihood of birthing a baby with a heart defect. According the most recent estimates, 1 in 5 women are obese at the time of conception.

Previous research has found that obesity in women during pregnancy can have adverse health consequences for both mother and child. Obesity increases a woman’s risk for contracting preeclampsia, or pregnancy-induced hypertension, gestational diabetes, and the need for cesarean delivery.

Babies born to women who were obese when they became pregnant also have a greater risk for being overweight and for developing type 2 diabetes throughout their life. Studies have also indicated a relationship between maternal obesity and birth defects. The most common type of birth defect is in fact congenital heart problems, which afflict 8 out of 1000 babies born in this country. These problems can range from minor to life-threatening.

In the current study, published in the American Journal of Clinical Nutrition, researchers examined maternal data collected over the course of 11 years on nearly 7400 children born with birth defects in the state of New York. Obesity was measured by using body mass index (BMI) calculations.

Comparing these records with mothers whose children were born without birth defects, investigators determined that mothers with BMIs that were 30 or above had a 15% higher likelihood of having a baby with a heart defect. When mothers were morbidly obese, which coincides with a BMI over 40, the risk for having a child with a heart defect increased to 33%. This increase was progressive and rose with each increase in BMI. Women who were considered overweight (BMI of 25 to 29.9) had no increase in risk.

One interesting point not factored into the findings was whether or not a woman who was obese, but lost weight before conceiving, reduces the risk of her child having birth defects. This scenario wasn't considered because the study was done after the babies were born. Doctors would have had to enroll previously obese women and study the frequency of heart defects in their babies to control for this factor. Nevertheless, the authors feel that until such a study can be conducted, the current findings support the value of losing weight before conceiving as a way of not only increasing the chances of having a health baby, but as a way of protecting the mother as well.

Another point to consider is that in some instances, being overweight or obese can inhibit a woman’s ability to become pregnant. Polycystic ovary syndrome (PCOS) is a condition linked to obesity and causes hormonal and metabolic problems that can result in irregular menstruation. This, in turn, can affect a woman’s ability to conceive.

If you are trying to become pregnant and have concerns about your BMI, speak with your physician. For more information about PCOS, visit the website for Women’s Health, a branch of the U.S. Department of Health and Human Services.