Oocyte maturation and pregnancy outcomes in relation to gonadotropin duration in antagonist cycles

Gonadotropin (Gn) stimulation duration is a modifiable factor in antagonist protocols, yet its association with oocyte maturation and pregnancy outcomes remains unclear. This study aimed to determine whether Gn duration is independently associated with oocyte maturation and pregnancy outcomes after controlling for key confounders and to identify an optimal Gn window in GnRH antagonist cycles with fresh embryo transfer.

This retrospective study included 9372 GnRH antagonist cycles at Xiangya Hospital. Multivariable regression models adjusting for confounders were used to assess the associations of Gn duration with oocyte maturation and pregnancy outcomes. Subgroup analyses were stratified by ovarian response. Generalized additive models were employed to identify nonlinear trends, followed by segmented and LOESS regression to determine the optimal duration.

After comprehensive adjustment, Gn duration maintained a significant nonlinear association with oocyte maturation (adjusted OR 1.07, 95% CI 1.05-1.09, p < .001), plateauing at approximately 9 days. Each additional stimulation day before 9 days was associated with increased maturation odds (adjusted OR 1.11, 95% CI 1.06-1.17; p < .001), while extended duration beyond 9 days showed no significant benefit (adjusted OR 0.94, 95% CI 0.88-1.01; p = .08). This association was absent in very low responders (≤5 oocytes) but consistent across other response subgroups. The 8-10 day duration window was associated with the highest likelihood of pregnancy and live birth.

In GnRH antagonist cycles, Gn duration is associated with oocyte maturation and pregnancy outcomes following fresh embryo transfer, even after adjusting for key confounders. The 8-10 day Gn window represents a range associated with the highest likelihood of clinical pregnancy and live birth. These findings support prioritizing dynamic, response-adapted stimulation protocols aimed at achieving trigger criteria within this window, rather than adhering to fixed duration targets.