Prepregnant weight in relation to risk of neural tube defects

Women who are obese before pregnancy may increase their baby's chance of developing a neural tube defect (NTD). An example of a NTD is spina bifida, which occurs when the spinal column does not completely close over the spinal cord. Researchers used a database of medical records on babies born with NTDs that also recorded the mother's pre-pregnancy weight. A total of 604 babies born with NTD were identified and their mother's pre-pregnancy weight was compared to the pre-pregnancy weight of the mothers of 1,658 babies born with other birth defects. The risk of having a baby with NTD increased as the mother's pre-pregnancy weight increased. Women over 110 kilograms before pregnancy were four times more likely to have a baby with NTD than women who weighed between 50 and 59 kilograms. Folic acid supplements did not reduce the obese women's chances of having a baby with NTD.
Objective.--To examine the relation between prepregnant weight and the risk of neural tube defects (NTDs). Design.--Data were collected from 1988 to 1994 in a case-control surveillance program of birth defects. Setting.--Study subjects were ascertained at tertiary care centers and birth hospitals in the greater metropolitan areas of Boston, Mass, and Philadelphia, Pa, and in southeastern Ontario. Participants.--Cases were 604 fetuses or infants with an NTD identified within 6 months of delivery. Controls were 1658 fetuses or infants with other major malformations identified within 6 months of delivery. For 1992 to 1994, there were 93 control infants without major malformations. Main Outcome Measure.--Relative risk of NTDs in infants or fetuses for different maternal weights. Results.--Relative to women who weighed 50 to 59 kg, risk of NTDs increased from 1.9 (95% confidence interval [Cl],1.2 to 2.9) for women weighing 80 to 89 kg to 4.0 (95% C1,1.6 to 9.9) for women weighing 110 kg or more. When women were classified according to daily intake above or below the recommended level of 400 [mu]g of folate, approximate threefold increases in risk were estimated for the heaviest weights in both groups. Intakes of 400 [mu]g of folate or more reduced risk of NTDs by 40% among women weighing less than 70 kg, but no risk reduction was observed among heavier women. Conclusion.--The risk of NTDs increased with increasing prepregnant weight, independent of the effects of folate intake.