TUESDAY, Feb. 10, 2009 (HealthDay News) -- If you're planning on becoming pregnant, a new study suggests that you should try to shed any extra weight you're carrying before conception.
That's because babies born to obese mothers are more likely to have serious birth defects.
"We found that being obese in pregnancy can increase a woman's risk of having a range of birth defects," said study senior author Judith Rankin, a reader in maternal and perinatal epidemiology at Newcastle University in Newcastle upon Tyne, United Kingdom.
"A further finding is that women who are overweight may also be at an increased risk, although the research evidence is not so clear and further work is needed," she noted.
Results of the study were published in the Feb. 11 issue of the Journal of the American Medical Association.
It's long been known that obesity in pregnancy can lead to gestational diabetes, high blood pressure, an increased risk of blood clots, a higher risk of infection and an increased risk of Cesarean delivery. Babies born to obese mothers are at risk of being too large and have an increased risk of perinatal death.
Maternal obesity has also been linked to the development of congenital anomalies, such as neural tube defects, spina bifida, heart defects, cleft lip and palate, and anencephaly (a defect in brain development). Birth defects are a leading cause of still birth and infant mortality, causing as many as one in five infant deaths in the United States, according to background information in the study.
To better assess this association, Rankin and her colleagues reviewed nearly 2,000 studies that included information on pre-pregnancy or early pregnancy weight and birth defects. They included 39 studies in their review.
Together, the pooled risk of having a baby with a neural tube defect was 87 percent higher for obese mothers compared to normal weight women. The risk of spina bifida was increased more than twofold. The odds of an infant having hydrocephaly (water on the brain) was upped by 68 percent for obese moms, and the odds of heart problems went up by 30 percent.
Rankin said the exact mechanism by which obesity would contribute to birth defects isn't known, but the researchers have several theories. One is that undiagnosed diabetes in the mothers may be contributing to these defects; another is that there may be nutritional deficiencies in the obese women, such as a lack of folic acid; and the final theory is that because ultrasound is more difficult to perform on heavy women, birth defects may not be seen early in pregnancy.
Rankin pointed out that the absolute risk of an obese woman having a baby with a birth defect is still low. "Birth defects occur in between 2 and 4 percent of all pregnancies, so the risk, even in obese women, remains low. If a woman who is obese is thinking of having a baby, the most important thing is to speak to their doctor and to think about their weight and diet so that they eat healthily and sensibly," she said.
Dr. Miriam Greene, an obstetrician at New York University Langone Medical Center in New York City, agreed that women need to make sure they're eating right as they start thinking about pregnancy, no matter what their current weight. And, she said, while it would be ideal if all women were at the proper weight before pregnancy, that's not always going to happen.
"Try to be in the best physical and emotional condition as possible before pregnancy," she advised. "That means you should have excellent nutrition, you should be exercising and come in for pre-pregnancy counseling."
Learn more about having a healthy pregnancy from the U.S. Centers for Disease Control and Prevention.