Endometrial thickness after ovarian stimulation with gonadotropin, clomiphene, or letrozole for unexplained infertility, and association with treatment outcomes.

Objective To study the association of endometrial thickness (EMT) with live birth rates (LBR) in ovarian stimulation with intrauterine insemination (OS-IUI) treatments for unexplained infertility. Design Prospective cohort analysis of the Reproductive Medicine Network's Assessment of Multiple Intrauterine Gestations from Ovarian Stimulation (AMIGOS) randomized controlled trial. Setting Multicenter randomized controlled trial. Patients A total of 868 couples with unexplained infertility (n=2,459 cycles). Interventions OS-IUI treatment cycles (n = 2,459) as part of the AMIGOS clinical trial. Main Outcome Measures Live birth rates; unadjusted and adjusted risk ratios (RR) for live birth by EMT category, calculated using generalized estimating equations. Results The overall mean EMT on day of human chorionic gonadotropin administration in cycles with a live birth was significantly greater than in those without. Compared to the referent EMT group of 9 to 12 mm, the unadjusted RR for live birth for the EMT groups of ≤5 and 6-8 were 0.48 and 0.92, respectively. The test for trend indicated evidence of decreasing LBR with decreasing EMT. After adjustment for ovarian stimulation medication, a linear trend was no longer supported. Stratified analyses revealed no differences in associations by treatment group. Conclusions In OS-IUI for unexplained infertility, higher LBR are observed with increasing EMT; however, EMT is not significantly associated with LBR when adjusted for OS treatment type. Appreciable LBR are seen at all EMT, even those of ≤5 mm, suggesting that OS-IUI cycles should not be canceled for thin endometrium. Clinical Trial Registration Number NCT01044862.