Gonadotrophin type and antral follicle count-adjusted follicular recruitment and oocyte yield in 4525 antagonist cycles.

Do FSH types (recombinant FSH [rFSH] versus highly purified human menopausal gonadotrophin (HP-HMG) versus corifollitropin alfa (CFA) differ in the efficiency of ovarian response, as assessed by follicular output rate (FORT) and follicle-to oocyte index (FOI)? Retrospective cohort study analysing 4525 antagonist IVF and intracytoplasmic sperm injection cycles using CFA (n = 728), rFSH (n = 1848) or HP-HMG (n = 1949). The FORT and FOI indices were calculated as ratios of follicle or oocyte yield to antral follicle count (AFC). Generalized estimating equations were used to account for clustering by patient with covariates for age, anti-Müllerian hormone (AMH), weight, stimulation duration, gonadotrophin dose and elective freeze. The CFA yielded the highest ovarian response indices (FORT 16-22 [61.6%], FOI-COC [106.4%], FOI-MII [81.1%]), compared with rFSH (49.3%, 98.0%, 74.6%) and HP-HMG (39.6%, 71.5%, 46.5%). Stratified analyses confirmed this ranking across AMH strata. In low AMH (<1.1 ng/ml), FOI-MII was 81.4% with CFA, 64.5% with rFSH and 49.2% with HP-HMG. In normal/high AMH (1.1-3 ng/ml) FOI-MII was 86.3%, 64.5% and 53.1%. Generalized additive model analyses demonstrated a modest non-linear AMH effect only for CFA, peaking at about 1.5-2.0 ng/ml before declining, whereas rFSH rose gradually and HP-HMG remained quite flat. Age-stratified analyses showed a uniform decline across FSH types. The risk of OHSS (>18 follicles ≥11 mm) was lowest with CFA (6.5%), compared with 19.8% for HP-HMG and 39.2% for rFSH. After adjusting for AFC, CFA achieved the highest FORT and FOI across most AMH strata, consistently outperforming HP-HMG and matching or exceeding rFSH, while maintaining the lowest follicle-count-based OHSS risk.