Pregnant women who are overweight with moderately elevated blood sugar never set off any alarms for their physicians. The big concern was for women who were obese or who had gestational diabetes because those conditions are known to cause a host of health risks to the mom and baby.

But a new study shows these women who are just above average for weight and blood sugar are at a higher risk of bad pregnancy outcomes than previously known. In fact, this group is at higher risk than pregnant women who are obese with normal blood sugar or pregnant women who have gestational diabetes and a normal weight.

"These are women who have not been on our radar because they don't have gestational diabetes and aren't obese, but our study shows if you are one step away from each of those, you carry some significant risks," said principle investigator Boyd Metzger, M.D., a professor of medicine-endocrinology at Northwestern University Feinberg School of Medicine and a physician at Northwestern Memorial Hospital. "We need to address the combination of overweight and blood sugar of these women as urgently as we do for women who are obese or have gestational diabetes."

This group of women comprised about 6 percent of the total number of women in the study. Obese women made up 16 percent of the group and those with gestational diabetes accounted for 13.7 percent.

The study also found women who are both obese and have gestational diabetes are at a much higher risk of having an adverse pregnancy than women having only one of those conditions.

The paper, published in the April issue of Diabetes Care, is from the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study and includes 23,316 women from nine countries.

One of the adverse outcomes for these mothers is having large babies, the result of fat accumulation. Large babies increase the risk of injury to the baby during vaginal delivery, increasing the likelihood of a Caesarean section.

The study found when the mothers are obese and have gestational diabetes, the babies weigh 340 grams more than babies of mothers with normal weight and blood sugar. When the mothers are overweight (but not obese) with above-average blood sugar levels, the babies weigh 214 grams more. Mothers of normal weight but with gestational diabetes have babies who weigh 164 grams more. And obese mothers with normal glucose levels have babies with an increased weight of 174 grams.

A pregnant woman's higher blood sugar level and weight also can lead to higher insulin and lower blood sugar levels in a newborn. In turn, these effects may eventually trigger obesity and diabetes, perhaps as early as childhood.

"The big message from this is when you look at the impact of nutrition, metabolism and weight on pregnancy outcomes, every woman - on her first prenatal visit -- should get a prescription for a session with a dietician and an appropriate healthy eating plan for her pregnancy," said Metzger, also the Tom D. Spies Professor of Metabolism and Nutrition at Northwestern's Feinberg School. "This doesn't happen, but it should, and insurance companies should reimburse it."

The research is supported by the National Institutes of Health.