Obesity and Fertility: A Prospective Cohort Study

Abstract

Background and Hypothesis: Previous studies have linked body mass index (BMI) with time to pregnancy. The objective of this analysis was to determine if obesity (BMI > 30 kg/m2) is associated with reduced fertility in a cohort of women who discontinued contraceptive method to attempt conception. We hypothesized that BMI is associated with time to conception after controlling for potential confounding variables. Methods: We performed a secondary analysis of the FACT (Fertility After Contraceptive Termination) study. We included 432 women, aged 18-35 years old, who discontinued contraception in an effort to conceive, were sexually active with a male partner, had the ability to consent, and had a minimum of 12 months of follow-up data. Participants were excluded who were already pregnant, had a history of infertility or medically induced sterility or, used depot medroxyprogesterone acetate (DMPA) in the past 5 months. We collected participant data on demographic, reproductive, medical characteristics, and sexual history, as well as date of contraceptive termination. We used Cox proportional hazard models to assess associations between BMI and time to conception while controlling for race, socioeconomic status, and prior contraceptive method. Results: A BMI of 30 or greater was associated with reduced fertility compared to participants with a BMI of less than 25 after controlling for race, low SES, and prior contraceptive method (HRadj=0.72; 95% CI 0.53, 0.97; p=0.03). We also noted that obese women with regular menses had reduced fertility compared to normal weight participants with regular cycles (HRadj 0.58; 95% CI 0.39, 0.86, p=0.007). For participants with irregular menstrual cycles, BMI was not associated with time to conception. Conclusion & Potential Impact: Our study supports the association of obesity with reduced fertility and increased time to conception. Future studies of weight loss should be considered as a method to improve conception rates.