Increasing a mother’s intake of folic acid by adding the vitamin to food supplies has been shown to cut the risk of having a baby with neural tube defects, a birth defect in which the spine doesn’t fuse properly. However, new research indicates that this benefit is much weaker in overweight and obese women.

“These women may either need higher doses of folic acid or they possess another risk factor related to obesity - e.g. mild, undetected diabetes mellitus - that amplifies their risk of neural tube defects, and it is independent of the preventive benefits of folic acid,” Dr. Joel G. Ray from University of Toronto, Ontario, Canada told AMN Health.

As reported in the medical journal Obstetrics & Gynecology, Ray and colleagues examined whether the risk of neural tube defects changed after the introduction of Canada’s folic acid fortification program in 1997.

In the heaviest women, the program cut the risk of neural tube defects by 44 percent. In contrast, in lighter women, the program reduced the risk by up to 90 percent.

Prior to fortification, the heaviest women were 40 percent more likely to have a neural tube defect-affected baby than their lean peers, whereas afterward, the increased risk jumped to 280 percent.

“All women should continue to take folic acid tablet supplements before pregnancy, and women who are overweight should consider a small degree of weight reduction before pregnancy,” Ray said. “This may lower her risk of having a neural tube defect-affected pregnancy, as well as the forms of high blood pressure and diabetes that are also related to obesity in pregnancy.”

“Long-term maintenance of a normal weight, beyond pregnancy, would seem to be one of the most important interventions for maintaining a woman’s health over the many years that follow pregnancy,” he suggested.

SOURCE: Obstetrics & Gynecology, February 2005.