Optimizing timing for intrauterine insemination (IUI) in donor sperm cycles: pre- versus post-ovulation insemination in natural cycles.

Purpose: To investigate whether pregnancy outcomes of natural cycle intrauterine insemination (IUI) with donor sperm can be improved by performing insemination after confirmation of ovulation.

Methods: This retrospective cohort study evaluated 751 couples undergoing 1170 cycles of artificial insemination with donor sperm (AID) in natural cycles between January 2018 and January 2021. Patients underwent AID either within 6-12 h after spontaneous luteinizing hormone (LH) surge (pre-ovulation group) or after ovulation was confirmed by ultrasound (post-ovulation group). Propensity score matching was performed to account for differences in baseline characteristics between groups. The main outcome measures of this study were clinical pregnancy rate and live birth rate.

Results: After propensity score matching, each group comprised 216 cycles. No significant differences were observed between the pre-ovulation and post-ovulation groups in terms of clinical pregnancy rate (30.6% vs 27.3%, respectively, p = .458) and live birth rate (25.0% vs 22.7%, respectively, p = .651). However, upon excluding cases of luteinized unruptured follicle syndrome (LUFS) from the pre-ovulation group, the clinical pregnancy rate (33.5% vs 27.3%, respectively, p = .043) and live birth rate (27.4% vs 22.7%, respectively, p = .039) were significantly higher in the pre-ovulation group.

Conclusions: For fertile women undergoing AID in natural cycles, pre-ovulation insemination timing yielded superior pregnancy outcomes compared to post-ovulation insemination when ovulation was achieved. However, due to the occurrence of LUFS, pre- and post-ovulation AID resulted in comparable overall pregnancy outcomes in natural cycles.