By Anne Harding
"Probably of all the maternal exposures and conditions that might be associated with birth defects, diabetes is the one that has the strongest association," lead investigator Dr. Adolfo Correa of the Centres for Disease Control and Prevention in Atlanta, told Reuters Health in an interview. The finding is particularly concerning, he added, given the worldwide epidemic of type 2 diabetes that shows no sign of abating any time soon.
Maternal type 1 and type 2 diabetes are known risk factors for birth defects involving the heart, brain, spinal cord and musculoskeletal system, he and his colleagues note in their report. But studies have shown, they add, that diabetic women with good blood glucose control during pregnancy are no more likely to have a baby with birth defects than non-diabetic women.
Gestational diabetes, or diabetes that appears for the first time during pregnancy, has also been linked to birth defects, Correa and his team point out, but it's not clear if this is because these women already had diabetes but it had simply not been diagnosed.
To better understand how birth defects relate to pre-pregnancy diabetes and gestational diabetes, the researchers looked at mothers of 13 030 babies born with birth defects and moms of 4 895 infants born without diabetes were malformations. They investigated risks for 39 different birth defects such as heart defects, lip and cleft palate, and limb malformations.
Overall, the researchers found, the women with pre-pregnancy at more than triple the risk of having a child with one or several birth defects. The relationship was actually stronger for infants with several birth defects.
Women with gestational diabetes were 42-percent more likely to have a baby with a single birth defect and at 50 percent increased risk of having a child with multiple malformations, but this relationship was largely limited to women who were overweight or obese.
This suggests, Correa said, that overweight women diagnosed with gestational diabetes probably were diabetic before becoming pregnant. It's unlikely that diabetes occurring only in pregnancy would be related to birth defects, he added, because it occurs late in gestation, when foetal organ systems are already formed.
More than half of pregnancies among diabetic women are unplanned, the researcher noted, and women who aren't planning on getting pregnant are likely to be less vigilant about keeping their blood glucose under control. He suggested that all women with diabetes who are of childbearing age talk with their doctor about getting into a preconception health care program, and take 400 micrograms of folic acid on a daily basis. This nutrient has been shown to prevent birth defects of the spinal cord and brain.
"There are many women with diabetes who do have normal babies," he added, "Primarily because they do have good control of their glucose."