A pregnant woman’s higher blood sugar level is linked to a significantly greater long-term risk of obesity in her child — even more than a decade later, reports a large new international study led by Northwestern Medicine. The higher the woman’s blood sugar, the greater the risk of her child being obese.

“The mother’s blood sugar level during pregnancy is an independent contributor to the child’s weight and risk of being obese later in childhood,” said corresponding study author Dr. Boyd Metzger, professor emeritus of medicine in endocrinology at Northwestern University Feinberg School of Medicine.

“We’ve known for a long time that family characteristics predict a lot about how you’re going to look, how fat a child will be, how tall he will be. This is above and beyond the mother’s weight. This takes into account all those other factors.”

Mothers with higher-than-normal blood sugar during pregnancy — even if not high enough to meet the definition for gestational diabetes commonly used in the U.S. today — also were significantly more likely to have developed type 2 diabetes a decade after pregnancy than their counterparts without high blood sugar.

The study was published in JAMA on Sept. 11.

Researchers have known that treating high blood sugar during pregnancy reduces problems for the newborn and mother. Lowering a mother’s blood sugar reduces the birth weight of the child, as well as the risk of pre-eclampsia, a potentially life-threatening condition in which the mother has high blood pressure that affects her and the baby.

But prior to this study, scientists did not know that risks related to blood sugar during pregnancy continue into childhood. And they still don’t know if treating the mother reduces these longer-term risks. Future studies will need to help answer these questions, Metzger said.

“We don’t know the mechanisms of how these long-term changes happen,” Metzger said. “We suspect epigenetic changes are likely to be influencing these long-term outcomes and those changes begin quite early in pregnancy.”

With major increases in obesity in the population worldwide, the frequency of all forms of diabetes, including gestational diabetes, has increased. New criteria based on the results of Metzger’s original HAPO Study in 2012 further increases the number of women with gestational diabetes.

The HAPO-FUS (Hyperglycemia and Adverse Pregnancy Outcomes-Follow-Up Study) evaluated children 10 to 14 years after birth in 10 clinical centers in seven countries: U.S., Canada, Israel, U.K., Hong Kong, Thailand and Barbados. The study included 4,697 moms and 4,832 children.

Investigators used multiple methods to determine degrees of overweight or fatness in the child. Simply calculating Body Mass Index (BMI) in kids has some limitations because a muscular young person will have a fairly high BMI but is not fat.

Clinical sites used a bod pod that more accurately calculates the percent of fat tissue. In addition, investigators measured the waist or hip as well as the thickness of the skin folds, which all correlate with how obese someone is, Metzger said.

“The children of moms with gestational diabetes and higher blood sugar were higher in all these categories,” Metzger said.

“The HAPO-FUS results are important because they demonstrate that even women with mild hyperglycemia during pregnancy and their offspring are at risk of harmful maternal and child health outcomes, potentially increasing the number of women and children at risk of acquiring lifelong chronic medical conditions,” said study coauthor Dr. Wendy Brickman, an associate professor of pediatric endocrinology at Feinberg and a pediatrician at Ann and Robert H. Lurie Children’s Hospital of Chicago. “Research is needed to identify interventions that will improve the health outcomes of these women and children.”

HAPO-FUS was funded under National Institute of Diabetes and Digestive and Kidney Diseases grant 1U01DK094830, with additional support from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, all of the National Institutes of Health.