Women who gain excessive weight or develop diabetes during pregnancy are more likely to have obese children even when the babies start out at a normal size, a U.S. study suggests.
Previous research has linked greater pregnancy weight gain and blood sugar spikes - a hallmark of diabetes - to higher odds of having an overweight newborn. But the current study offers some of the first evidence that these factors can increase the obesity risk even in even healthy weight infants.
Researchers followed more than 13,000 normal weight babies for a decade.
About 49 percent were overweight at some point between ages 2 and 10, and 29 percent were obese, they found.
Children were about 29 percent more likely to be obese by age 10 when their mothers had diabetes during pregnancy, and they had 16 percent higher odds of obesity when their mother's pregnancy weight gain exceeded 40 pounds.
"It is a common belief that all normal weight babies have the same risk of becoming obese as children and adults," said lead study author Dr. Teresa Hillier of the Kaiser Permanente Center for Health Research in Portland, Oregon and Honolulu, Hawaii.
"This study shows that that isn't true," Hillier added by email.
When pregnant women gain lots of weight or develop diabetes, it may trigger a process Hillier calls "obesity imprinting" that leads the baby to adapt to an overfed environment in the womb and alters its long-term metabolism.
Hillier and colleagues found that during pregnancy, 20 percent of the mothers had gained more than 40 pounds. Doctors recommend that normal weight women gain 25 to 35 pounds during pregnancy.
About 12 percent of the women had abnormal results from a diabetes screening during pregnancy known as a glucose tolerance test but didn't develop diabetes.
Another 5.5 percent of the mothers in the study had what's known as gestational diabetes, the type developed during pregnancy, researchers report in Maternal and Child Health Journal.
One shortcoming of the study is that researchers lacked data on how heavy women were before they got pregnant, the authors note. This could influence the results because obese mothers are more likely than normal weight women to have overweight and obese children.
Overweight or obese women who shed excess pounds before they become pregnant can lower the likelihood of having an obese child, noted Dr. Joachim Dudenhausen, a researcher at Weill Cornell Medicine in New York and Charite University Medicine Berlin who wasn't involved in the study. Gaining less weight during pregnancy, or treating gestational diabetes, can also lower the risk of childhood obesity.
One common myth women need to avoid is the notion that pregnancy is a time they can "eat for two," Dudenhausen added by email.
"It is not necessary, moreover it is dangerous, to eat for two, as my grandmother was told about nutrition during pregnancy," Dudenhausen said.
Once babies are born, even a mother who gained too much pregnancy weight or developed gestational diabetes can still take steps to lower the odds of obesity for her children, Hillier noted.
"She can breastfeed her infant; studies show that breastfed babies are less likely to become obese and we also found breastfeeding reduced childhood obesity in a small subsample of our study," Hillier said.
"She can also feed her child healthy foods, and get nutritional advice about what to feed her baby, especially when it comes to starting on solid food, and she can make sure her she and her child get plenty of exercise."