Comparison of Pregnancy Outcomes in Ovulatory Frozen Transfer Cycles With or Without Trigger and Non-Ovulatory FET...

This study aimed to evaluate and compare the pregnancy outcomes in ovulatory frozen embryo transfer (FET) cycles, with or without an ovulation trigger, against non-ovulatory FET cycles. The goal was to identify whether utilizing the natural ovulatory process, either spontaneous or medically induced, yields better clinical outcomes rather than relying entirely on hormone replacement therapy for endometrial preparation, focusing on pregnancy rates, ongoing clinical pregnancies, and early pregnancy losses.

This was a single-centre retrospective cohort analysis. A total of 1490 first-time FET cycles were analyzed. Patients undergoing a first FET cycle with a single vitrified and warmed blastocyst for transfer were stratified based on their FET preparation cycle for comparison. Patients were grouped into non-ovulatory FET cycles (group A, n = 1061), ovulatory FET cycles with ovulation trigger (group B, n = 328), and ovulatory FET cycles without trigger (group C, n = 101). The primary outcomes assessed were pregnancy rates (determined by positive beta-human chorionic gonadotropin) and ongoing pregnancy rates (based on detecting a fetal heartbeat at 7 weeks). Secondary outcomes included miscarriage rates. Statistical significance was evaluated using analysis of variance and χ² tests (P < 0.05).

Pregnancy rates were comparable between all groups, with 50.3% in group A, 54.9% in group B, and 52.5% in group C (P = 0.35). Ovulatory cycles (groups B and C) showed significantly higher ongoing pregnancy rates compared to non-ovulatory cycles (P = 0.02). The miscarriage rate was higher in group A (17.0%) compared to group B (8.9%) and group C (11.3%), though this difference did not reach statistical significance (P = 0.07).

Ovulatory FET cycles, whether triggered or not, result in significantly higher ongoing pregnancy rates and lower miscarriage rates compared to non-ovulatory cycles. These findings support the preservation of the natural ovulatory process, either through spontaneous or induced ovulation, as a key factor in improving clinical outcomes in assisted reproductive technologies. The study highlights the potential advantages of modified natural cycles over artificial cycles that rely solely on exogenous hormone supplementation.