Neural Tube Defect Risk Persists in Babies of Overweight Mothers

Folic acid fortification of flour does not overcome the increased risk of open neural tube defects (NTDs) in the offspring of overweight mothers.

Dr. Joel G. Ray from University of Toronto, Ontario, stated that "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 NTDs, and it is independent of the preventive benefits of folic acid."

Dr. Ray and colleagues examined whether the risk of open NTD, in relation to maternal obesity, changed after the introduction of Canada’s folic acid fortification program in 1997.

Before fortification, maternal weights in the highest quartile (compared with the 3 lower quartiles) were associated with a 40% increase in the risk of NTD, the authors report, whereas after fortification, the risk was 2.8 times that of women whose weight was in the lower 3 quartiles.

When stratified by weight, the reduction in the odds of NTD associated with folic acid fortification was only 44% for women with weights in the 4th quartile, the researchers note, compared with reductions of 68%, 70%, and 90% for women with weights in the 1st, 2nd, and 3rd quartiles, respectively.

Overall, each 10-kg increase in maternal weight was associated with a 20% increase in the risk for NTD, the report indicates.
"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 (such as 2-3 kg) before pregnancy," Dr. Ray said. "This may lower her risk of having a NTD-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.
Obstet Gynecol 2005;105.