Association between ovarian sensitivity index and IVF-ET outcomes in women of advanced maternal age.

OBJECTIVE: To investigate the association between the ovarian sensitivity index (OSI) and ovarian responsiveness, embryo quality, and pregnancy outcomes in women of advanced reproductive age (≥35 years) undergoing IVF-ET. METHODS: This retrospective cohort study included 1,055 fresh embryo transfer cycles performed at the Reproductive Medicine Center of Yulin Maternal and Child Health Hospital between January 1, 2021, and December 31, 2023. Patients were stratified by OSI tertiles: low (≤2.174, n=353), middle (2.174- 4.103, n=351), and high (>4.103, n=351). Multivariable logistic regression was used to adjust for confounders and assess the independent association between OSI and clinical pregnancy. RESULTS: No significant differences were observed in infertility duration, BMI, LH, E2, T, P, or endometrial thickness on HCG day (all P>0.05). The high OSI group was younger with lower FSH and higher AMH/AFC (P<0.05), required less Gn and shorter stimulation, and yielded more oocytes, 2PN embryos, available embryos, and high-quality Day 3 embryos (P<0.05). Implantation and clinical pregnancy rates were higher in the high OSI group (P<0.05), but no differences were seen in live birth, multiple pregnancy, or early miscarriage rates (all P>0.05). Of note, the live birth rate - the most clinically meaningful endpoint in IVF - did not differ significantly across OSI tertiles (P = 0.412), indicating that the higher clinical pregnancy rates in the high OSI group did not translate into a higher live birth rate. After adjustment for age, FSH, AMH, and AFC, OSI tertiles were not independently associated with clinical pregnancy (overall P = 0.357). Age (OR = 0.880, 95% CI: 0.833-0.930, P<0.001) and AMH (OR = 1.114, 95% CI: 1.002-1.238, P = 0.046) remained independent predictors. CONCLUSION: In univariate analysis, higher OSI was associated with ovarian responsiveness, embryo quality, and clinical pregnancy rates; however, it is not independently associated with clinical pregnancy after adjustment for confounding factors, particularly age and AMH. OSI may serve as a composite indicator reflecting ovarian responsiveness and embryo quality, but should be interpreted in conjunction with age, AMH, and other relevant clinical factors.