Impact of Body Fat Distribution and Insulin Sensitivity on In Vitro Fertilization Outcomes: A Prospective Observational Study

Background: Since overweight is increasing worldwide, the interest in its potential impact on fertility treatment has increased. Whilst the body mass index (BMI)-based overweight classification is simple, BMI cannot measure body fat distribution. In this research, we aim to investigate whether waist circumference (WC) and waist-to-hip ratio (WHR) are better predictors of ovarian response in IVF cycles than BMI. Methods: This prospective observational study included 265 couples undergoing their first IVF/ICSI treatment. BMI, WC, WHR, and insulin sensitivity (measured with homeostatic model assessment (HOMA) index) were assessed at enrollment. The primary outcome of the study was the correlations between the study variables and the ovarian sensitivity index (OSI), calculated according to the formula [(number of retrieved oocytes/total gonadotropin dose) × 1000]. Secondary outcomes were other IVF-related outcomes, including live birth rates. Results: The study included 265 women with a mean age of 35.8 ± 4.4 years. The mean BMI was 24.0 ± 4.2 kg/m2, WC was 79.1 ± 10.8 cm, and WHR was 0.85 ± 0.09. WC was >80 cm in 102 women and ≤80 cm in 163; WHR was >0.85 in 146 women and ≤0.85 in 119. Higher WC and WHR were both significantly associated with lower OSI, independent of BMI. OSI was lower in women with a WC of >80 cm vs. ≤80 cm (3.2 ± 2.5 vs. 4.6 ± 3.9, p < 0.05) and in those with a WHR of >0.85 vs. ≤0.85 (3.4 ± 2.3 vs. 4.9 ± 4.1, p < 0.05). Live birth rates did not differ between groups. Conclusions: The type of body fat distribution is associated with the ovarian response to controlled ovarian stimulation. In particular, upper body fat correlates negatively with ovarian sensitivity to exogenous gonadotropins. However, potential effects on live birth rates do not seem to be clinically relevant.