Diabetes, folic acid intake affect fetal risk of birth defects

The risk of birth defects for children of diabetic mothers is influenced by both the mother’s diabetes and her intake of folic acid around the time of conception.

Clinicians should encourage all patients contemplating pregnancy to initiate prophylactic folic acid supplementation.

Not taking vitamins or supplements containing folic acid around the time of conception may double the risk of heart and noncardiac birth defects among the offspring of women with diabetes mellitus, according to the findings of a multicenter, population-based case-control study.

Researchers from the Centers for Disease Control and Prevention conducted the National Birth Defects Prevention Study, which included approximately 20,000 affected and control infants. Children with birth defects were stratified into 18 groups with various heart defects and 26 groups with noncardiac birth defects.

The results reveal a pattern of odds ratios suggestive of at least a nonstatistically significant 2-fold greater risk of birth defects among the offspring of diabetic women who didn’t take folic acid-containing vitamins periconceptionally versus those who did. The pattern held true for approximately 75% of the birth defects studied. In addition, they found an association between preexisting diabetes mellitus and an increased risk of birth defects, regardless of periconceptional use of supplements containing folic acid.

But the authors were quick to note that the diabetic women who used supplements likely planned their pregnancies and so were more likely to maintain better glycemic control periconceptionally than diabetic women who did not use supplements. Good glycemic control can reduce the increased risk for birth defects to rates similar to those of nondiabetic women.

It is difficult to know whether any apparent synergistic relationship between diabetes and the lack of folic acid supplementation reflects differences in pregnancy planning and glycemic control or is a pure effect from the lack of a folic acid-containing supplement. 

The authors conclude that because the risk of birth defects among diabetic women remains high, any prevention is welcome. Thus, all women of reproductive age should be encouraged to consume vitamin supplements containing folic acid.

The study was published in the American Journal of Obstetrics and Gynecology (2012;206[3]:218.e1-218.e13).

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