The Significance of Serum CA-125 Level on the Live Birth Rates of In Vitro Fertilisation in Women with Endometriosis

<i>Background and Objectives</i>: To evaluate the significance of serum CA-125 level on the live birth rate of in vitro fertilization (IVF) in women with endometriosis. <i>Materials and Methods</i>: This retrospective observational study included women with endometriosis who underwent one stimulated IVF cycle. Serum CA-125 levels were measured in archived serum samples collected prior to ovarian stimulation, on the day of ovulation trigger, and during frozen embryo transfer. Serum CA-125 levels were compared between cycles with and without a live birth in both stimulated IVF and frozen embryo transfer cycles, with a subgroup analysis using a cut-off of 35 IU/L. <i>Results</i>: Within the same patient undergoing the same IVF cycle, serum CA-125 level on the trigger day of the stimulated cycle was significantly lower than the baseline level before stimulation started (35.1 IU/L [21.0-64.5 IU/L] vs. 46.8 IU/L [25.9-104.0 IU/L], <i>p</i> < 0.001), but was higher than that in the frozen embryo transfer cycles (31.7 IU/L [19.9-58.7 IU/L] vs. 27.3 IU/L [18.1-59.9 IU/L], <i>p</i> = 0.041). Serum CA-125 levels were not associated with the live birth rate in the stimulated IVF cycle and frozen embryo transfer cycles. In subgroup analysis, women with serum CA-125 level ≥ 35 IU/L on the trigger day had a significantly higher pregnancy rate from the fresh embryo transfer cycle than those with level < 35 IU/L (adjusted odds ratio 4.126, 95% CI 1.241-13.720, <i>p</i> = 0.021). The cut-off of 35 IU/L did not show significant differences in live birth rate for either stimulated or frozen embryo transfer cycles. <i>Conclusions</i>: In women with endometriosis, no significant differences in serum CA-125 levels were found between those with and without a live birth in fresh and frozen embryo transfer cycles. In fresh embryo transfer cycles, those with serum CA-125 ≥ 35 IU/L had significantly higher pregnancy rates.