OBJECTIVE: To estimate the effect of body mass index (BMI) on oocyte and embryo parameters and cycle outcomes in women undergoing in vitro fertilization (IVF).
METHODS: We evaluated a retrospective cohort of 1,721 women undergoing a first IVF cycle with fresh, autologous embryos between 2007 and 2010 in an academic infertility practice. Main outcome measures included number of mature and normally fertilized oocytes, embryo morphology, estradiol on the day of human chorionic gonadotropin administration, clinical pregnancy, spontaneous abortion, and live birth. We performed multivariable analyses, adjusting for potential confounders, including age at cycle start, infertility diagnosis, type of stimulation, total gonadotropin dose, use of intracytoplasmic sperm injection, and number of embryos transferred.
RESULTS: Compared with women of normal BMI, women with class II (BMI 35–39.9) and III (BMI 40 or higher) obesity had fewer normally fertilized oocytes (9.3 compared with 7.6 and 7.7, P<.03) and lower estradiol levels (2,047 pg/mL compared with 1,498 and 1,361, P<.001) adjusting for age and despite similar numbers of mature oocytes. Odds of clinical pregnancy (odds ratio [OR] 0.50, 95% confidence interval [CI] 0.31–0.82) and live birth (OR 0.51, 95% CI 0.29–0.87) were 50% lower in women with class III obesity as compared with women of normal BMI.
CONCLUSION: Obesity was associated with fewer normally fertilized oocytes, lower estradiol levels, and lower pregnancy and live birth rates. Infertile women requiring IVF should be encouraged to maintain a normal weight during treatment.
LEVEL OF EVIDENCE: II