Weight gain between pregnancies may increase the risk of stillbirth or infant death, a new study from Sweden suggests.
The researchers analyzed information from more than 450,000 women who had two pregnancies between 1992 and 2012.
Women whose body mass index (BMI) increased by more than 4 points between pregnancies were about 50 percent more likely to have stillbirths in their second pregnancies than women whose weight was stable between pregnancies. Four BMI points is the equivalent of gaining about 24 lbs. (11 kilograms) for a woman of average height.
In addition, among mothers who were a normal weight in their first pregnancies (with a BMI of less than 25), a weight gain of about 13 to 24 lbs. (6 to 11 kg) before the second pregnancy was linked with a 27 to 60 percent greater risk of infant death in the first year of life for the second pregnancy.
Weight gain between pregnancies was not linked with infant death for women who were already overweight in their first pregnancies. But overweight women who lost more than 13 lbs. (6 kg) between their first and second pregnancies had a 50 percent lower risk of infant death in the first month of the child's life, compared with overweight women who maintained their weight between pregnancies.
The findings could have "substantial public health implications," given that about 15 percent of women in the study experienced weight gains of at least 13 lbs. before their second pregnancies, said the researchers, from the Karolinska Institute, a medical university in Stockholm, Sweden. The results "emphasize the need to prevent weight gain before pregnancy in healthy and overweight women, and that weight loss should be promoted in overweight women," the researchers wrote today (Dec. 2) in the journal the Lancet. [9 Uncommon Conditions That Pregnancy May Bring]
It's important to note that a woman's overall risk of stillbirth or infant death is still relatively low. Among women who remained a stable weight between pregnancies, two out of 1,000 had a stillbirth and two out of 1,000 had an infant death. Among women who gained at least 24 lbs. between pregnancies, four out of 1,000 had a stillbirth and three out of 1,000 had an infant death.
In the study, stillbirth was defined as death of the fetus at 28 weeks of pregnancy or later.
The researchers said they aren't sure why weight gain between pregnancies would increase the risk of stillbirth or infant death. But being overweight or obese is known to increase the risk of preterm birth and birth defects, which are major contributors to infant morality. Obesity and weight gain can increase inflammation in the body, which in turn might lead to potentially harmful pregnancy outcomes, such as having one's water break early, the researchers said.
The findings held true even after the researchers took into account other factors that could affect the risk of stillbirth and infant death, including the mother's age, smoking habits and time between pregnancies. However, the researchers were not able to account for a women's diet or alcohol consumption during pregnancy, which could affect her risk of poor pregnancy outcomes, the researchers said.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.