High serum FSH levels on day 7 of stimulation are negatively associated with oocyte retrieval in GnRH antagonist protocols: real-world evidence from 9,969 IVF cycles in China

This study aimed to investigate how levels of serum follicle-stimulating hormone (FSH) on Day 7 of ovarian stimulation are related to the number of oocytes retrieved, and identify any cutoff or threshold point in protocols using gonadotropin-releasing hormone (GnRH) antagonists. We examined data from January 2017 to June 2024, covering 9,969 cycles from 7,981 patients using GnRH antagonists as part of in vitro fertilization processes. We found a complex link between serum FSH and oocyte collection. Lower serum FSH on Day 7 was associated with collection of fewer oocytes (β = −0.531, p < 0.0001), and different levels were associated with changes in the number of oocytes collected. The key point was 9.13mIU/mL. If serum FSH exceeded 9.13 mIU/mL on Day 7, each 1mIU/mL increase reduced the number of oocytes collected by 0.07 (effect β = −0.07, 95% confidence interval [CI] −0.10 to −0.05, P < 0.0001). When serum FSH was below 9.13 mIU/mL, each 1 mIU/mL rise increased the number of oocytes collected by 1.18 (effect β = 1.18, 95% CI 0.95 to 1.41, P < 0.0001). This association suggests that it may be possible to improve ovarian reaction by raising the FSH dose if serum FSH is under 9.13 mIU/mL. However, if serum FSH is already over 10 mIU/mL, it seems likely that other steps may be needed to increase ovarian reaction, although these hypotheses will need to be tested in future studies.