Results
Among 821 cycles that were started between 2012 and 2020 and in which a single frozen-thawed, euploid blastocyst embryo transfer strategy was applied, most women were of normal weight (BMI, 18.5-25 kg/m2, n=602). A total of 80 of the cycles involved underweight women with a low BMI (BMI < 18.5 kg/m2), 112 of the cycles involved overweight women (BMI, 25-30 kg/m2), and 27 of the cycles involved obese women (BMI ≥ 30 kg/m2). The baseline characteristics of participants are presented in Table 1. There was a significant difference in endometrial thickness in FET between groups, with overweight women more likely to have thicker endometrium. Infertility type and protocol in fresh cycle differed significantly across the four groups, with obese women more prevalent with more primary infertility and agonist protocol. The overweight women had a higher rate of clinical pregnancy rate. However, there were no other specific differences in fertility parameters between different BMI categories.
Univariate analysis was performed to evaluate each variable’s effect on live birth rate (Table 2). Female age in fresh cycle was negatively associated with live birth, while agonist protocol was positively associated with live birth. Interaction and stratified analyses were shown in Table S1. There were no significant interactions in any of the subgroups (p>0.05 for all comparisons).
Figure 1 shows the spline-transformed association of BMI with live birth, and BMI tended to be linearly associated with live birth. Figure S1 shows NGS PGT cycle outcomes from the year 2012 to 2020. Figure S2 shows survival rates from 2012 to 2020. Multivariate logistic regression failed to show a statistically significant relationship between BMI and live birth in underweight (BMI < 18.5 kg/m2; adjusted odds ratio [AOR] 0.80; 95% confidence interval [CI], 0.47-1.35, p=0.402), overweight (BMI 25-30 kg/m2: AOR 0.85; 95% CI, 0.54-1.35, p=0.491), and obese patients (BMI≥ 30 kg/m2: AOR 1.07; 95% CI, 0.48-2.38, p=0.864) compared with the normal weight reference group (Table 3).