Higher live birth rates are associated with normal BMI in PGT-A FET cycles: a SART CORS study

To determine if body mass index (BMI) was associated with live birth in patients undergoing transfer of frozen-thawed preimplantation genetic testing for aneuploidy (PGT-A) embryos.Retrospective cohort study of cycles reported to Society for Assisted Reproductive Technology Clinic Outcomes Reporting System (SART CORS).All autologous and donor recipient PGT-A tested cycles reported to SART CORS from 2014 to 2017.Body mass index (BMI).The primary outcome measure was live birth rate and secondary outcome measures were clinical pregnancy and biochemical pregnancy rates. Multivariable Generalized Additive Mixed Models (GAMM) and log-binomial models were used to model the relationship between BMI and outcome measures.A total of 77,018 PGT-A cycles from 55,888 patients were analyzed. Of these cycles, 70,752 were autologous and 6,266 were donor recipient. In autologous cycles, a statistically significant and clear non-linear relationship was observed between BMI and live birth rates, with the highest birth rates observed for the BMI range of 23-24.99 kg/m2. When using 23-24.99 kg/m2 as the referent, other BMI ranges demonstrated a lower probability of live birth and clinical pregnancy that continued to decrease as the BMI became further from the reference value. Patients with BMI <18.5 had 11% lower probability of live birth, whereas patients with a BMI of ≥40 had 27% lower probability compared to the referent.Normal weight BMI in the range of 23-24.99 kg/m2 was associated with the highest probability of clinical pregnancy and live birth following a frozen-thawed PGT-A tested blastocyst transfer in both autologous and donor recipient cycles. BMI outside the range of 23-24.99 kg/m2 is likely associated with a malfunction in the implantation process, which is presumed to be related to a uterine factor and not an oocyte factor, as both autologous and donor recipient cycle outcomes were associated similarly to the BMI of the intended parent.