The risk of stillbirth increases linearly with interpregnancy weight gain, according to a Swedish population-based cohort study.
The researchers found that between-pregnancy weight gain greater than four body mass index units – about 11 kg or 24 lbs – was associated with more than a 50% increase in stillbirth risk in a second pregnancy, even after controlling for confounders such as maternal education and smoking.
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The Swedish study of 456,711 women who had their first and second singleton births between 1992 and 2012 showed an increased risk of infant mortality for women who had a healthy weight in their first pregnancy and then gained weight. For those that gained between two and four body mass index (BMI) units, the relative risk was 27%, compared with stable weight women. There was a 60% increased risk of infant mortality among women who gained more than four BMI units, according to the findings published online in the Lancet on Dec. 2.
Each BMI unit corresponds to about 2.8 kg (6 lbs) in an average height woman (167 cm, or 5 feet 5 inches).
Already overweight women did not show an increased risk of infant mortality with weight gain, but did show significantly reduced infant mortality with weight loss greater than two BMI units between pregnancies (relative risk 0.49; 95% confidence interval, 0.27-0.88). But that same weight loss in healthy-weight women increased the risk of infant mortality (Lancet. 2015 Dec 2. doi: 10.1016/S0140-6736(15)00990-3).
“Obesity and weight gain are associated with inflammatory upregulation, and inflammation has been proposed as one mechanism for the associations between maternal overweight and obesity and several adverse pregnancy outcomes,” wrote Dr. Sven Cnattingius, from the Karolinska Institute, Stockholm, and Dr. Eduardo Villamor from the University of Michigan, Ann Arbor.
The study was supported by the Swedish Research Council for Health, Working Life and Welfare, and the Karolinska Institute. The researchers reported having no financial disclosures.