Progestin-only pretreatment enhances follicular synchronization and embryo development: a three-arm retrospective cohort study in GnRH antagonist cycles

Hormonal pretreatment prior to controlled ovarian stimulation (COS) in assisted reproductive technology (ART) is widely used to improve follicular synchronization and schedule flexibility. However, the comparative impact of different pretreatment strategies—progestin-only, combined oral contraceptive pills (COCP), and no pretreatment—on follicular dynamics and clinical outcomes remains unclear. In this retrospective cohort study, 240 patients undergoing their first IVF/ICSI cycle with a GnRH antagonist protocol and recombinant FSH monotherapy were analyzed. Participants were divided into three groups: progestin-only pretreatment (P group), COCP pretreatment (COCP group), and no pretreatment (control group). Baseline characteristics, follicular development, embryo quality, and cumulative reproductive outcomes were compared. Levene’s test was used to assess follicular size variability, and multivariable regression analyses were performed to adjust for confounding variables. The P group demonstrated significantly improved follicular synchronization, as evidenced by the lowest variability in the ratio of follicles ≥ 18 mm to ≥ 14 mm. Embryological outcomes were superior in the P group, with higher oocyte maturation rate (p = 0.040), fertilization rate (p = 0.038), and number of good-quality blastocysts (p = 0.015) compared to the other groups. The blastocyst development rate was also significantly greater (p = 0.029). Although cumulative live birth rate (CLBR) did not reach statistical significance, a trend toward higher CLBR was observed in the P group (87.0%) compared to COCP (72.0%) and control (75.2%). Progestin-only pretreatment leads to superior follicular synchronization and improved embryo developmental potential in GnRH antagonist IVF/ICSI cycles. These benefits may enhance ART efficiency and contribute to improved cumulative outcomes.