Association between menstrual cycle length and ovarian reserve markers and stimulation response: a retrospective cohort study.

AIM: To evaluate the relationship between menstrual cycle length (MCL) categories and ovarian reserve biomarkers and controlled ovarian stimulation (COS) response levels. MATERIALS AND

METHODS

Medical records of women undergoing infertility evaluations between January 2022 and April 2025 were reviewed. A total of 550 women undergoing fresh IVF/ICSI cycles were screened for eligibility, and 440 normo-ovulatory women who met all inclusion criteria were included. Patients were grouped according to MCL (21–28 and 29–35 days). Demographic characteristics (age, body mass index), baseline hormonal parameters (anti-Müllerian hormone (AMH), cycle day-3 follicle-stimulating hormone, luteinizing hormone, and estradiol), and antral follicle count (AFC) were recorded. COS outcomes including the number of retrieved and metaphase II (MII) oocytes, follicular output index (FOI), and follicle-to-oocyte index (FORT) were documented. Fertilization was achieved via IVF or ICSI, and embryo transfer was performed on days 2–5.

RESULTS

AMH levels were significantly lower in the MCL (21–28 days) group than in the MCL (29–35 days) group (p < 0.001). AFC levels were significantly lower in the MCL (21–28 days) group than in the MCL (29–35 days) group (p = 0.003). The number of oocytes developed after stimulation was significantly lower in the MCL (21–28 days) group than in the MCL (29–35 days) group (p < 0.001). The number of MII oocytes was significantly lower in the MCL (21–28 days) group than in the MCL (29–35 days) group (p < 0.001). The clinical pregnancy rate was significantly lower in the MCL (21–28 days) group than in the MCL (29–35 days) group (p = 0.017).

CONCLUSION

Within the normal range of MCLs, longer cycles are associated with higher AMH and AFC levels and greater oocyte yields after controlled ovarian stimulation. Although women with longer cycles showed higher crude clinical pregnancy rates, MCL was not an independent predictor of clinical pregnancy once ovarian reserve markers were accounted for. These findings suggest that MCL is a simple, history-based indicator of underlying ovarian reserve and ovarian response.