Carpinello OJ, Jahandideh S, Yamasaki M, et al. - Researchers conducted a retrospective cohort study comparing clinical and ongoing pregnancy after natural cycle (NC) intrauterine insemination (IUI) vs ovarian stimulation (OS) IUI in ovulatory women undergoing therapeutic donor insemination (TDI). Examining a total of 76,643 IUI cycles in patients treated with intrauterine insemination, they included women undergoing TDI in the absence of diagnosed female factor infertility. Interventions included use of clomiphene citrate or letrozole in NC TDI or OS TDI with either clomiphene citrate or letrozole. From 2,343 patients (711 patients without repeated IUI cycles), 6,192 TDI cycles met inclusion criteria and were analyzed (3,837 NC and 2,355 OS). Findings revealed a < 4% increase in clinical and < 1% increase in ongoing pregnancy, and more than fourfold increase in ongoing multiple gestations in correlation with ovarian stimulation in TDI cycles. Based on findings, they emphasize considering natural cycle IUI as a first-line treatment for ovulatory women who require donor insemination.