background: Limited data exist concerning the need for luteal support in clomiphene citrate-stimulated intrauterine insemination (IUI) cycles. The addition of progesterone became an established clinical practice, despite the absence of evidence of effectiveness. methods: A prospective randomized controlled trial was performed in a tertiary referral centre to assess the effect of intravaginal micronized progesterone as luteal support on the probability of ongoing pregnancy in patients stimulated

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... with clomiphene citrate for IUI. Normoovulatory women, ≤36 years of age, undergoing ovarian stimulation with clomiphene citrate (50 mg) for IUI (n ¼ 468) were randomized during the period from September 2008 to December 2009. Patients were randomized, either to receive luteal phase support (n ¼ 243) in the form of vaginal micronized progesterone in three separate doses (200 mg, 3 times a day), or to the control group who did not receive luteal phase support (n ¼ 225). results: Data from 400 women were analysed. Following the first interim analysis, the study was prematurely cancelled as an extremely low total pregnancy rate was found. No difference was observed in ongoing pregnancy between patients who did, or did not, receive vaginal progesterone as luteal support [8.7% (17/196) versus 9.3% (19/204), respectively, P ¼ 0.82; difference 20.6%, 95% confidence interval (CI): 26.4, 5.2]. Additionally, the early pregnancy loss rate did not differ between groups (1.5% progesterone group versus 2% no progesterone group, P ¼ 0.78; difference 20.5%, 95% CI: 23.6, 2.7). conclusions: Routine supplementation of the luteal phase with vaginal progesterone does not seem to improve pregnancy rates in normo-ovulatory women stimulated with clomiphene citrate for IUI. Clinical trials.gov:NCT01046708.