Natural cycle frozen-thawed embryo transfer in young women with regular menstrual cycles increases the live-birth rates compared with hormone replacement treatment: a retrospective cohort study

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 = 308), or hormone treatment (HT) for patients who could not be frequently monitored (n = 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.