The effect of low body mass index (BMI) on ooctye quality in IVF cycles

Abstract

OBJECTIVE: Prior studies examining the impact of low body mass index (BMI) on in vitro fertilization (IVF) outcomes have shown conflicting results with some demonstrating lower pregnancy rates and others showing no difference compared to normal weight women. We previously demonstrated that women with a low BMI have a significantly higher prevalence of poor quality oocytes. The aim of this study was to determine if women with a low BMI have poorer pregnancy outcomes with IVF compared to normal weight women and determine if underweight women produce poorer quality oocytes or embryos in an expanded cohort. DESIGN: Cross-sectional study. MATERIALS AND METHODS: Data for 422 women undergoing their first IVF or oocyte cryopreservation cycle at a single center between 2011-2012 were analyzed. Participants were classified into two groups based on BMI < 19 kg/m2 (n=69) and 19.1-25 kg/m2 (n=353). The primary outcome was clinical pregnancy rate. Secondary outcomes included the number of oocytes retrieved, fertilization rate, blastulation rate, implantation rate and ongoing pregnancy rate. A secondary analysis for oocyte quality was done of 301 women who had the cumulus cells removed from the oocytes at the time of oocyte retrieval. Oocytes described as being granular or having vacuoles, dark cytoplasm, debris or inclusions were considered poor quality. Logistic and count regression analyses adjusted for age, day 3 FSH and ethnicity were used to determine the association between BMI and outcomes of interest. RESULTS: When controlling for age, day 3 FSH and ethnicity the clinical pregnancy rates were not different between underweight and normal weight women (37% vs. 41%, P=0.68). The multivariate model confirmed being underweight was associated poor oocyte quality (31% vs. 18%, P=0.05) and a trend towards fewer oocytes retrieved (10.6 vs. 12.1, P=0.08) in the expanded cohort. There were no differences in the fertilization rate, blastulation rate, implantation rate or ongoing pregnancy rates between the two groups. CONCLUSION: Underweight women have a significantly higher prevalence of poor quality oocytes and a strong trend toward fewer oocytes retrieved compared to normal weight women. The poor quality of the oocytes did not significantly impact embryo development or pregnancy rates in underweight women undergoing IVF.