A mother's blood-sugar level during pregnancy may be a powerful — but easily controllable — contributor to childhood obesity, according to a large new study by researchers with Kaiser Permanente's Center for Health Research (CHR). The study, published in the September issue of Diabetes Care, found that mothers with untreated gestational diabetes — a form of the disease that occurs only during pregnancy — were nearly twice as likely to bear overweight children, compared with healthy moms. And the data showed that some mothers with "normal" blood-sugar readings were at risk as well: pregnant women with blood-sugar levels at the highest end of the currently accepted normal range were at least 22% more likely to have heavy children than women in the lowest quartile.
Researchers analyzed medical information on 9,439 mother-child pairs who received health care through Kaiser Permanente in the Pacific Northwest and Hawaii. All women gave birth between 1995 and 2000, and none had pre-existing diabetes. The women were screened for hyperglycemia, or high blood sugar, and gestational diabetes; their children were measured for weight between the ages of 5 and 7 — what researchers call the adiposity-rebound period, during which excessive weight gain usually predicts adult obesity. Regardless of factors like race or ethnicity, birth weight and maternal weight gain or age, researchers found that the risk of a child becoming overweight rose in step with the mother's blood-sugar level during pregnancy.
Women whose blood-sugar tests indicated gestational diabetes were 89% more likely than other women to have overweight children, and 82% more likely to have obese kids. Women whose blood-sugar readings were at the upper end of normal (122 mg/dl to 140 mg/dl) were still 22% more likely to have overweight children than women at the low end of normal (with blood-sugar levels between 43 mg/dl and 94 mg/dl), and 28% more likely to bear children who become obese. "Even in what's considered normal, in the highest quartile there was an elevation in risk," says Dr. Teresa Hillier, a CHR endocrinologist and senior investigator and lead author of the study. "You could argue, should we consider lowering the criteria? One forty [mg/dl] is the typical cutoff [for diabetes]. Some ppl have argued that it should be 130."
Previous studies, mostly in the Pima Indian population, have shown a link between a mother's diabetes and obesity in her children. Hillier's study is the first, however, to suggest that treatment of the disease eliminates risk. In her analysis, Hillier found that children born to women with the highest levels of blood sugar were no likelier than other kids to become heavy if their mothers had been treated for diabetes during pregnancy.
Doctors believe that maternal diabetes increases children's obesity risk through what's referred to as metabolic imprinting. The idea is that outside of other genetic and environmental risk factors for obesity, children appear to become metabolically imprinted, or pre-programmed, for obesity by being overfed in the womb — a direct result of the mother's high blood sugar. "As we have more people with diabetes and gestational diabetes during pregnancy I think the importance of additional risk factors for obesity increases," says Hillier. "And if there is an alteration going on to program the child for obesity I think that starts a vicious cycle for obesity in a way."
The American Diabetes Association, which funded the current study, estimates that 1% to 14% of pregnant women will develop gestational diabetes; on average the figure rests at about 5% to 7%. Risk factors for the condition are similar to those for diabetes outside of pregnancy: family history for diabetes, being overweight and older age. Race and ethnicity also increase risk; the condition is more common among most non-Caucasians. Treatment for gestational diabetes begins with diet and exercise; failing that, patients are given insulin.
Women typically get screened for hyperglycemia at weeks 24 to 28 of their pregnancy, but the test is not universally given. Hillier encourages mothers-to-be to talk to their doctors about diabetes risk, insist on getting screened and, most importantly, to work out a treatment plan if necessary. "In sticking with treatment, women not only improve their outcome during pregnancy, but also in the long term for their child," she says.