Objective To assess the effects body mass index (BMI) on live birth rates in patients undergoing in vitro fertilization (IVF) with trophectoderm biopsy and preimplantation genetic testing for aneuploidies (PGT-A) when transferring a single euploid blastocyst. Design Retrospective cohort study. Setting Public fertility center in China. Population 821 women who underwent first cycle of frozen-thawed single euploid blastocyst transfer between 2012 and 2020. Methods Patients were grouped by World Health Organization (WHO) BMI class: underweight (<18.5, n=80), normal weight (18.5-24.9, n=602), overweight (25-30, n=112), and obese (≥30, n=27). A logistic regression model was used to assess the association between BMI and live birth while adjusting for potential confounders. Main outcome measures Live-birth rate was primary outcome. Results There was no difference in the birth weight, miscarriage, preterm birth, pregnancy complication, type of delivery and fetal gender by BMI category. The clinical pregnancy rate was higher in the overweight and obese groups. In multivariate logistic regression analysis, we fail to demonstrate a statistically significant relationship between BMI and live birth in underweight (adjusted odds ratio [AOR] 0.80; 95% confidence interval [CI], 0.47-1.35, p=0.402), overweight (AOR 0.85; 95% CI, 0.54-1.35, p=0.491) or obese (AOR 1.07; 95% CI, 0.48-2.38, p=0.864) patients compared with the normal weight reference group. Conclusion No statistically significant relationship was identified between BMI and live birth in patients undergoing IVF with PGT-A, suggesting that the negative impact of obesity on IVF and clinical outcomes may be related to aneuploidy.

Objective To compare the effectiveness of natural cycles (NC) and artificial cycles (AC) in women undergoing frozen-thawed embryo transfer (FET) after in vitro fertilization (IVF). Design Retrospective cohort study. Setting Public fertility center in China. Population We studied 9733 women undergoing the first cycle of FET over a 3-year period (June 2014 - December 2017). All women were followed-up until one year after embryo transfer. Methods The type of endometrial preparation was determined by the treating physician’s preference, based on patients’ characteristics. Women with regular ovulation were allocated to natural cycles (n=1676), while patients who were reluctant to frequently monitoring or living far from the hospital were allocated to artificial cycles (n=8057). A logistic regression model was used to assess the association between endometrial preparation and clinical outcomes while adjusting for potential confounders. Main outcome measures Live-birth rate was primary outcome while miscarriage rate, clinical pregnancy rate, preterm birth rate, and ectopic pregnancy rate were secondary outcomes. Results In the adjusted model, type of endometrial preparation did not affect live birth (OR, 0.89; 95%CI, 0.79-1.01), clinical pregnancy (OR, 0.96; 95%CI, 0.85-1.09), preterm birth (OR, 1.09; 95%CI, 0.90-1.33) and ectopic pregnancy (OR, 0.77; 95%CI, 0.36-1.61), while AC significantly increased the miscarriage rate (OR, 1.38; 95%CI, 1.11-1.73, P=0.004). Conclusion In women undergoing FET, natural cycles and artificial cycles resulted in comparable live birth rate while miscarriage rate was higher in artificial cycles.