Received July 19, 2022
Accepted December 02, 2022

Objective: To relate the difference between the interval (days) until menstruation in a fixed dosage of estradiol in the luteal phase with the recently stated rate of follicular maturation (FORT) in ICSI cycles with GnRH antagonist. Methods: We retrospectively studied 66 ICSI cycles in women aged ≤39 years who received 4mg/day estradiol starting on the twenty-first day of the luteal phase for seven days, controlling transvaginal ultrasound on the second day of the cycle. The interval until the onset of the stimulus defined three groups: one day (n = 19), two to five days (n = 32) and ≥ 6 days (n = 15). Stimulus was initiated when endometrium ≤ 5 mm and CFA (> 3 to 10mm diameter) was held. The antagonist was added when a follicle ≥ 14mm. The oocyte retrieval occurred 35-36h post-hCG and embryo transfer on day 3. Results: There were significant differences in groups 1 and 3 related to the average duration of stimulation, total gonadotropin and basal FSH. The basal levels of estradiol showed a significant difference among the three groups, with higher levels respectively in groups 1, 2 and 3. There were no differences in total ampoules of antagonist, oocytes, M2 oocytes and FORT (primary outcome). The same applied to the number of embryos transferred of good quality and pregnancy rate per transfer. Conclusion: Our preliminary data showed no statistically significant difference compared to FORT between groups. The full study will include 268 cycles, with 90% power to demonstrate this difference.