Hormone replacement versus natural frozen embryo transfer for euploid embryos.

The goal of this study is to investigate hormone replacement (HR) versus natural frozen embryo transfer outcomes for euploid embryos. This is a retrospective cohort study at an academic medical center of patients undergoing in vitro fertilization with 24-chromosome day 5/6 preimplantation genetic testing for aneuploidies (PGT-A), from 2014 to 2018 using euploid single embryo frozen transfer. Multivariable logistic regression was used to study the association between transfer outcomes (ongoing pregnancy and miscarriage) with type of frozen euploid embryo transfer (HR versus natural) while controlling for multiple patient and cycle confounders. From a total of 389 cycles, 45.0% utilized HR frozen embryo transfer and 55.0% were natural cycles. We found that when compared to HR frozen embryo transfer, natural cycle frozen embryo transfer had significantly higher ongoing pregnancy rates (aOR 2.05, 1.27-3.31, p = 0.003). There was no significant difference in miscarriage rates between the two groups (aOR for natural 0.69, 95% CI 0.37-1.32, p = 0.27). When limiting the analysis to only the first transfer at our institution, findings were similar of higher ongoing pregnancy rates and no difference in miscarriage rates. In our multivariate analysis, we found that natural cycle single euploid frozen embryo transfer was associated with significantly higher ongoing pregnancy rates than HR transfer, with no difference in miscarriage rates.