The impact of changes in LH levels in flexible antagonist protocols on the clinical outcomes of fresh IVF/ICSI cycles in populations of POSEIDON groups 1 and 2: a retrospective cohort study

Objective To investigate the impact of changes in luteinizing hormone (LH) levels during ovulation induction using flexible gonadotropin-releasing hormone antagonist (GnRH-A) regimens in POSEIDON groups 1 and 2 on the clinical outcomes of fresh in-vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) cycles. Method A retrospective analysis was conducted on the clinical data of females in POSEIDON groups 1 and 2 who underwent IVF/ICSI using a flexible GnRH-A regimen at the Reproductive Medicine Center of Fujian Maternal and Child Health Hospital from January 2017 to December 2022. According to the values of change in LH [(LH level on the trigger day − baseline LH)/baseline LH] × 100%, the study subjects were divided into five groups. The general information, laboratory indicators, and clinical outcomes of each group were compared. Results In POSEIDON group 1, a significant difference was observed in terms of the number of retrieved eggs, mature eggs, fertilization number (two pronuclei (2PN) number), and cleavage among all groups (all P values < 0.05). In POSEIDON group 2, a significant difference was observed in terms of the number of retrieved eggs, mature eggs, fertilization number (2PN number), cleavage, excellent embryos, and blastocysts (all P values < 0.05). The number of eggs retrieved in group A was significantly lower than that in groups D and E ( P = 0.010 and 0.001, respectively). The number of mature eggs in group A was significantly lower than that in groups D and E ( P = 0.008 and 0.000, respectively). The number of mature eggs in group E was significantly higher than that in groups B and C ( P = 0.033 and 0.021, respectively). The 2PN number in group A was significantly lower than that in groups D and E ( P = 0.042 and 0.002, respectively). The cleavage count of group E was significantly higher than that of groups A and C ( P = 0.005 and 0.037, respectively). The excellent embryos in group B were significantly lower than those of group E ( P = 0.038). Conclusion The use of a flexible GnRH-A regimen to induce ovulation in the POSEIDON groups 1 and 2 can lead to better-controlled ovarian stimulation (COS) outcomes. This involves the LH level on trigger day decreasing within the range of 0–100% from baseline (with optimal range being ≥ −100% to −50%). This trend was more obvious in the POSEIDON group 2 population.