Impact of GnRH agonist trigger on subsequent follicular phase length in ART cycles.

RESEARCH QUESTION: Does the use of GnRH agonist trigger versus hCG trigger affect the length of the subsequent follicular phase in women?

DESIGN

A retrospective cohort study analyzing 196 women undergoing controlled ovarian stimulation with freeze-all for PGT-M at a university-affiliated fertility center; 132 received GnRH agonist trigger, and 64 received hCG trigger.

RESULTS

The GnRH agonist group demonstrated a significantly longer subsequent follicular phase compared to the hCG group (18.98 ± 3.54 vs. 16.06 ± 3.13 days, P < .001), with extended follicular phase occurring in 90.2% versus 60.9% of cycles (P < .001). Both groups had comparable antral follicle counts (14.52 ± 7.71 vs. 13.00 ± 15.36, P = .748). Multiple regression analysis identified GnRH agonist trigger as a significant independent predictor of subsequent follicular phase length (coefficient = 4.552, 95% CI: 3.058-6.045, P < .001), along with BMI (coefficient = 0.188, 95% CI: 0.019-0.357, P = .030). The model explained 31.4% of the variance in follicular phase length (F = 7.516, P < .001). After adjusting for confounding variables, pregnancy rates were comparable between groups (OR = 1.763, 95% CI: 0.798-3.505, P = .173).

CONCLUSIONS

The GnRH agonist trigger prolongs the subsequent follicular phase compared to the hCG trigger without compromising pregnancy rates. BMI showed a statistically significant but modest association with follicular phase length that requires further validation. These findings have important implications for optimizing the timing of frozen embryo transfer in subsequent cycles and may facilitate more personalized monitoring protocols.