High birth weight babies increase a child’s risk of becoming obese.

Women who gain a lot of weight during pregnancy are more likely to have high-birth-weight babies, which may increase the children’s risk of becoming obese later in life, a new study suggests.The findings add to growing evidence of the importance of appropriate weight gain during pregnancy.

For several decades, researchers have observed that a high birth weight increases the risk that a child will gain too much weight later in life. Some studies of animals suggest excess calories affect the fetus, including the fat tissue and the organs that regulate body weight.

Now researchers at Children’s Hospital in Boston and Columbia University in New York have studied the medical records of more than 500,000 women who had two or more pregnancies, a total of more than 1 million babies. A newborn who weighed more than 81/2 pounds at birth was considered at a high birth weight.

By comparing siblings, researchers for the first time were able to control for mothers’ genetic influences on birth weight.

The findings, reported online in The Lancet: The women gained an average of 30 pounds during pregnancy; those who gained 50 pounds were twice as likely to have a high-birth-weight baby than those who gained 20.

“Although birth weight is not the only determinant of adult weight, these findings suggest that an optimal time to begin obesity prevention efforts is before birth,” says pediatric endocrinologist David Ludwig of Children’s Hospital, lead author of the study.

Matthew Gillman of Harvard Medical School, who is also researching pregnancy and weight gain, says follow-up studies are needed to establish the link between gestational weight gain and childhood obesity.

In the meantime, there are other reasons to be concerned, Ludwig says. Pregnant women who are overweight or obese are at greater risk of problems such as complications during labor and delivery (including C-sections), gestational diabetes and high blood pressure.

A word of caution: “Being severely underweight during pregnancy, as well as severely limiting food intake, can also be problematic to fetal growth and development,” says Alan Fleischman, medical director for the March of Dimes, which works to improve babies’ health. Too little weight gain increases the risk of having a low-birth-weight baby of less than 51/2 pounds.

Via USA Today