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

## TL;DR

Using a GnRH agonist instead of hCG during fertility treatment leads to a longer follicular phase without affecting pregnancy rates.

## Contribution

The study shows that GnRH agonist triggers significantly prolong the follicular phase compared to hCG triggers in ART cycles.

## Key findings

- GnRH agonist trigger resulted in a significantly longer follicular phase (18.98 days) compared to hCG trigger (16.06 days).
- Pregnancy rates were comparable between the GnRH agonist and hCG groups after adjusting for confounding variables.
- BMI had a modest but statistically significant association with follicular phase length.

## Abstract

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

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.

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).

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.

GnRH agonist trigger prolongs the subsequent follicular phase by approximately five days compared to the hCG trigger without affecting pregnancy rates. This finding has important implications for FET cycle planning.