GnRH agonist early follicular challenge test as a predictor of ovarian response in antagonist cycles for fertility preservation

The aim of our study was to evaluate if the response to follicular GnRH agonist (GnRHa) trigger be used to predict intracycle ovarian response in GnRH antagonist cycles among women undergoing fertility preservation IVF. We conducted a prospective study of 146 GnRH antagonist oocyte pickup (OPU) cycles to evaluate GnRHa stimulation test (GAST). On day 2 of the cycle, basal E2 were measured, followed by injection of 0.2 mg GnRHa as part of the initial ovarian stimulation. 12 h later blood sampling was repeated (GAST E3). E2 response was used as test parameter. The major outcome was the number of mature cryopreserved oocytes. We found a linear correlation between both GAST E3 level and GAST E3/E2 ratio and number of M2 oocytes. ROC curve analysis of GAST E3, GAST E3/E2 ratio, AFC and day 3 FSH for > 15 M2 and < 5 M2 oocytes was calculated. For GAST E3 levels obtaining < 5 M2 oocytes, an AUC value of 0.79 was found. For GAST E3 levels obtaining > 15 M2 oocytes, AUC value of 0.8. Patients with GAST E3 ≤ 384 pmol/l has 58.6% risk to obtain < 5 oocytes. Patients younger than 35 with GAST E3 > 708 pmol/l have 66% chance for freezing > 15 oocytes. The response to single GnRHa administration during GnRH antagonist cycle can be used as biomarker of ovarian reserve. This simple, widely available marker, which reflect the estradiol response of small follicles, might predict the response of the specific cycle, and can potentially be used to adjust the treatment dose. Trial registration number: 0304-20-ASF.