Objective: To determine the optimal endometrial preparation protocols of frozen-thawed embryo transfer (FET) in young women with regular menstrual cycles. Design: Retrospective cohort study. Setting: Public fertility center. Patient(s): Infertile women with regular menstrual cycles undergoing FET. Intervention(s): Natural cycle (NC) treatment for patients with proven ovulation in previous cycles or who refused medication (n ¼ 308), or hormone treatment (HT) for patients who could not be frequently monitored (n ¼ 1,538). Main Outcome Measure(s): Live-birth rates. Result(s):The live-birth rates were 61.73% in the NC group and 55.11% in the HT group. The effect size of the endometrial preparation on live-birth rates was evaluated in prespecified and exploratory subgroups in each subgroup, and multivariable logistic regression analysis was used to determine which variables could be independently associated with the live-birth rate. The HT patients had a lower chance of live birth in all subgroups: endometrial thickness on the day of progesterone administration, triple-line endometrial pattern, female age at embryo transfer, fertilization type, and protocol in the fresh cycle. Multivariable analysis showed NC to be associated with an increased likelihood of live birth compared with HT. Conclusion(s): Natural cycle treatment has a higher chance of live birth than HT for endometrial preparation in young women with regular menstrual cycles. (Fertil Steril Ò 2020;113:811-7. Ó2019 by American Society for Reproductive Medicine.) El resumen está disponible en Español al final del artículo.

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It is unknown whether seasonal variation influences the outcome of in vitro fertilization (IVF). Previous studies related to seasonal variation of IVF were all small sample size, and the results were conflicting. We performed a retrospective cohort study evaluating the relationship between seasonal variability and live birth rate in the year of 2014–2017. Patients were grouped into four seasons (Winter (December-February), Spring (March-May), Summer (June-August), and Autumn (September-November)) according to the day of oocyte pick-up (OPU). Multivariate logistic regression analysis was performed to evaluate association between seasonal variation and live birth. Models were adjusted for covariates including temperature, sunshine hour, infertility type, infertility duration, infertility factor and BMI. In total 38,476 women were enrolled, of which 25,097 underwent fresh cycles, 13,379 were frozen embryo transfer. Live birth rates of fresh embryo transfer were 50.36%, 53.14%, 51.94% and 51.33% for spring, summer, autumn and winter, respectively. Clinical pregnancy rate between the calendar months varied between 55.1% and 63.4% in fresh embryo transfer (ET) and between 58.8% and 65.1% in frozen embryo transfer (FET) (P-values 0.073 and 0.220). In the unadjusted model and adjust model, seasonal variation was not associated with live birth. In conclusion, there was no significant difference of seasonal variations in the outcome of IVF with fresh embryo transfer and frozen embryo transfer.

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