Large population-based epidemiological studies have found that a high prepregnancy body weight or body mass index (BMI) increases the risk of many adverse maternal and perinatal complications including stillbirth. This prospective population-based study, based on the Swedish Birth Register, examined associations between a change in prepregnancy BMI between first and second pregnancies. The study population consisted of 151,025 women having their first two consecutive singleton births from 1992 to 2001. BMI was estimated at the first antenatal visit of each pregnancy.
Women in the study gained just over half a BMI unit on average during a mean inter-pregnancy interval of 2 years. After adjusting for potential confounding factors, the risk of adverse outcomes increased linearly with the amount of weight gained between pregnancies. Adjusted odds ratios with 95% confidence intervals for women gaining 3 or more BMI units were 1.78 (1.52–2.08) for preeclampsia; 1.76 (1.39–2.23) for gestational hypertension; 2.09 (1.68–2.61) for gestational diabetes; 1.32 (1.22–1.44) for cesarean delivery; 1.63 (1.20–2.21) for stillbirth; and 1.87 (1.72–2.04) for a large-for-gestational-age birth. Except for stillbirth, similar associations were confirmed in women whose BMI was less than 25 during both pregnancies. BMI status at the start of the first pregnancy did not significantly influence the effects of inter-pregnancy BMI change on the risks of preeclampsia, cesarean delivery, or stillbirth.
Inter-pregnancy weight gain correlates strongly with the risk of major maternal and perinatal complications, even in women who are not overweight. The findings implicate some nonmeasured obesity-related factor. The results of this large-scale trial provide a rationale for promoting weight loss in overweight and obese women who are planning to become pregnant. It is even more important for healthy-weight women not to gain weight before pregnancy.
Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts; and Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden