By Steven Reinberg
The finding held true whether or not a woman developed actual "gestational diabetes" during pregnancy, the researchers noted.
Babies might also be affected: Children born to these women were more prone to obesity, the study found.
"For mothers, high blood sugar is an important risk factor for later development of abnormal blood sugar levels, including type 2 diabetes," said researcher Dr. Boyd Metzger. He's professor emeritus of medicine at Northwestern University Feinberg School of Medicine in Chicago.
For the study, Metzger and colleagues used data from a national study that followed mothers and their children for 10 to 14 years after birth.
The results from the original study showed that modestly elevated blood sugar increases the rate of complications for the baby before and after birth.
The latest study compared the long-term effects of blood sugar levels in mothers who had gestational diabetes with those who didn't.
Metzger's team found that the harms of even modestly elevated blood sugar levels extended for both mother and child for more than a decade.
Among women with elevated blood sugar during pregnancy, nearly 11 percent had type 2 diabetes 10 to 14 years after giving birth, and about 42 percent had pre-diabetes, the findings showed.
Among women who did not have elevated blood sugar during pregnancy, about 2 percent had type 2 diabetes and just over 18 percent were pre-diabetic at follow-up.
In all, nearly 4,700 mothers were tested for type 2 diabetes, pre-diabetes or other problems related to blood sugar.
In addition, the researchers studied more than 4,800 children for overweight and obesity. The investigators found that 19 percent of the children born to mothers with elevated blood sugar levels were obese, compared with 10 percent of the children of mothers who had normal blood sugar levels.
However, the study did not prove that high blood sugar levels during pregnancy actually caused these health risks to rise in these women and their children.
Previous research has shown that a healthy lifestyle -- weight control and regular physical activity -- can greatly reduce development of diabetes in women who previously had gestational diabetes, Metzger said.
"It is important that all pregnant women be tested to identify those with gestational diabetes, and those with the condition should be treated during pregnancy. And mothers and children have good reasons to maintain a healthy lifestyle throughout their lifetime," he said.
Dr. Noelia Zork, a maternal-fetal medicine specialist at NewYork-Presbyterian-Columbia University Irving Medical Center, in New York City, said that pregnant women with gestational diabetes need to continue to manage their blood sugar and make lifestyle changes that will lower their risk of type 2 diabetes.
"I make it a point to my patients who are diagnosed with gestational diabetes to tell their primary care physician and follow-up every year to get tested for diabetes," she said.
Zork also said that infants exposed to high levels of sugar in the womb may suffer changes in the way their organs develop that permanently alter how they handle food, and that predisposes them to obesity in childhood.
"Also, women who are obese have a greater chance of having a child who is obese and obese as an adult," she added. "Having gestational diabetes on top of obesity increases that risk even more."
Zork believes that preventing gestational diabetes starts before pregnancy.
"Whenever I see a woman who is planning pregnancy, one of the things I talk about is her weight, so if she is either overweight or obese we discuss trying to lose maybe 5 percent of her weight before she gets pregnant," Zork said.
Women need to be in the best shape they can to ensure a healthy pregnancy for themselves and their baby, she explained.
The report was published Sept. 11 in the Journal of the American Medical Association.