Violet Kieu - Reproductive Services Unit, Royal Women’s Hospital, Melbourne, VIC, Australia. Department of Obstetrics and Gynaecology, The University of Melbourne, Melbourne, VIC, Australia. Melbourne IVF, Melbourne, VIC, Australia.
Alex Polyakov - Reproductive Services Unit, Royal Women’s Hospital, Melbourne, VIC, Australia. Department of Obstetrics and Gynaecology, The University of Melbourne, Melbourne, VIC, Australia. Melbourne IVF, Melbourne, VIC, Australia.
Genia Rozen - Reproductive Services Unit, Royal Women’s Hospital, Melbourne, VIC, Australia. Department of Obstetrics and Gynaecology, The University of Melbourne, Melbourne, VIC, Australia. Melbourne IVF, Melbourne, VIC, Australia.
Daniel Lantsberg - Reproductive Services Unit, Royal Women’s Hospital, Melbourne, VIC, Australia. Department of Obstetrics and Gynaecology, The University of Melbourne, Melbourne, VIC, Australia. Melbourne IVF, Melbourne, VIC, Australia.
Catharyn Stern - Reproductive Services Unit, Royal Women’s Hospital, Melbourne, VIC, Australia. Department of Obstetrics and Gynaecology, The University of Melbourne, Melbourne, VIC, Australia. Melbourne IVF, Melbourne, VIC, Australia.
Wan Tinn The - Reproductive Services Unit, Royal Women’s Hospital, Melbourne, VIC, Australia. Department of Obstetrics and Gynaecology, The University of Melbourne, Melbourne, VIC, Australia. Melbourne IVF, Melbourne, VIC, Australia.

Background: The use of frozen embryo transfers (FET) in assisted reproduction has increased worldwide. Controlled ovarian hyperstimulation in a fresh transfer may impair endometrial-embryo synchronicity. However, there is conflicting evidence on live birth rates (LBR) and clinical pregnancy rates (CPR). Objective: To compare LBRs and CPRs between single autologous day ۵ fresh vs. vitrified blastocyst transfer cycles, to investigate the impact of controlled ovarian hyperstimulation on embryo-endometrium asynchrony. Materials and Methods: A large cross-sectional analysis of ۶۰۰۲ embryo transfers (ET) comprised ۳۷۷۴ fresh and ۲۲۲۸ FET cycles from ۲۰۱۶ to ۲۰۱۹. Multivariate and subgroup analysis were performed for high responders (> ۲۰ oocytes). Results: Univariate analysis showed no difference in LBR (۲۸.۳% vs. ۲۷.۴%, p = ۰.۴۳) and CPR (۳۲.۲% vs. ۳۰.۹%, p = ۰.۳۰); however, multivariate analysis demonstrated significantly lower LBR (OR ۰.۸۶۴, p = ۰.۰۴۶, ۹۵% CI ۰.۷۴۹-۰.۹۹۷) and CPR (OR ۰.۸۵۲, p = ۰.۰۲۴, ۹۵% CI ۰.۷۴۲-۰.۹۷۹) in FET compared to fresh ETs. Younger participant age, previous in vitro fertilization pregnancy, advanced blastocyst expansion, higher trophectoderm quality, and lower cumulative number of ETs all improved the odds of LBR and CPR. Conventional in vitro fertilization, rather than intracytoplasmic sperm injection, improved CPR but not LBR. Body mass index affected neither LBR nor CPR. In the subgroup, multivariate analysis of high responders showed no difference in LBR or CPR. Conclusion: This study demonstrates relatively higher LBR and CPR of nearly ۱۴% for fresh ETs compared to FETs, in multivariate analysis. A universal freeze-all strategy, without appropriate indication, may lead to suboptimal outcomes. In high responders, freeze-all cycles may be beneficial, as outcomes appear similar.

Blastocyst, Live birth, In vitro techniques, Pregnancy rate, Vitrification, Reproduction., بلاستوسیست, تولد زنده, تکنیک­های آزمایشگاهی, میزان بارداری, انجماد, تولید­مثل.