W

omen who start out at a healthy weight but grow heavier after childbirth face an increased risk of infant mortality for their future children, according to a study published Wednesday in The Lancet.

The research looked at nearly half a million Swedish women and found that when mothers gained at least 13 pounds after a first pregnancy, their subsequent babies had a 50 percent higher risk of dying in the first year of life than the children of women who maintained a steady weight from one pregnancy to the next. As weight gain increased, the risk also increased. 

Even so, the absolute risk remained quite small. The elevated risk for mothers who put on pounds only equates to about two more infant deaths per 1,000 births.

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For women who are overweight to start with, it’s hugely helpful to neonatal outcomes if they lose weight before getting pregnant again, said study author Dr. Eduardo Villamor, an epidemiologist at University of Michigan.

Villamor said the finding will help doctors know when and how to discuss weight gain with their patients.

Women might want to look at “both controlling gestational weight gain in the previous pregnancy and actively losing weight before the next,” he said.

But Lisa Bodnar, a nutritional epidemiologist who wasn’t affiliated with the study, urged caution in extrapolating the results from Swedish women to the United States.

“American women are different, our health care system is different, our social inequalities are different,” said Bodnar, an associate professor at the University of Pittsburgh.

The findings do underscore previous research that found a link between excessive maternal weight and poor outcomes for mothers and babies. Some normal weight gain during pregnancy comes from new tissues — like the baby, placenta, and amniotic fluid — while additional weight gain, particularly in a woman’s body fat, could be tied to metabolic changes that crop up during pregnancy.

Bodnar said women often get good medical support and frequent doctor visits during pregnancy but not after childbirth, which can make it difficult for them to maintain a healthy weight.

She also noted that it’s not always realistic for women to get into optimal shape before pregnancy, because half of all pregnancies in the United States are unplanned.

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