Effect of overweight and obesity on live birth rate in single euploid frozen embryo transfers.

Research Question: Does endometrial preparation using a natural cycle lead to higher live birth rates (LBR) in single euploid frozen embryo transfers (FET) compared with programmed cycles, for women who are normal weight, overweight and obese.

Design: Retrospective study of 845 single euploid FETs from 688 couples. Patients were stratified by body mass index (BMI) into normal weight, overweight and obesity class I/II categories. Outcome was LBR.

Results: After achieving covariate (female age, anti-Müllerian hormone, embryo quality and infertility type) balance in each stratum, the effective sample size was 481 and 262 for the programmed cycles and natural cycles, respectively. The programmed cycle approach (vaginal luteal phase support with 3 × 100 mg micronized vaginal progesterone per day) was associated with significantly lower LBR in the weighted regression analysis of the cohort (RR 0.80, 95% CI 0.73 to 0.88, P < 0.001), compared with the natural cycle approach. The effect was significantly modified by BMI (P = 0.003 but was significant for all BMI categories. Reduction in live birth was less pronounced in patients with normal weight or who were overweight BMI (RR 0.87, 95% CI 0.78 to 0.97, P = 0.014) compared with patients with class I/II obesity (RR 0.61, 95% CI 0.49 to 0.75, P < 0.001).

Conclusions: A natural cycle endometrial preparation approach leads to overall better LBR in single euploid FET. The most significant difference is observed in women with higher BMI. Overweight or obese patients undergoing hormone replacement therapy may require a higher dosage of progesterone for luteal phase support.