Prepregnancy and Early Adulthood Body Mass Index and Adult Weight Change in Relation to Fetal Loss

OBJECTIVE: To examine prospectively the relationships of prepregnancy body mass index (BMI), BMI at age 18 years, and weight change since age 18 years with risk of fetal loss. METHODS: Our prospective cohort study included 25,719 pregnancies reported by 17,027 women in the Nurses' Health Study II between 1990 and 2009. In 1989, height, current weight, and weight at age 18 years were self-reported. Current weight was updated every 2 years thereafter. Pregnancies were self-reported, with case pregnancies lost spontaneously and comparison pregnancies ending in ectopic pregnancy, induced abortion, or live birth. RESULTS: Incident fetal loss was reported in 4,494 (17.5%) pregnancies. Compared with those of normal BMI, the multivariate relative risks of fetal loss were 1.07 (95% CI [confidence interval] 1.00–1.15) for overweight women, 1.10 (95% CI 0.98–1.23) for class I obese women, and 1.27 (95% CI 1.11–1.45) for class II and class III obese women (P trend≤.001). Body mass index at age 18 years was not associated with fetal loss (P trend=.59). Compared with women who maintained a stable weight (±4 kg) between age 18 years and before pregnancy, women who lost weight had a 20% (95% CI 9–29%) lower risk of fetal loss. This association was stronger among women who were overweight at age 18 years. CONCLUSION: Being overweight or obese before pregnancy was associated with higher risk of fetal loss. In women overweight or obese at age 18 years, losing 4 kg or more was associated with a lower risk of fetal loss. LEVEL OF EVIDENCE: II