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OBJECTIVE To study whether endometrial scratching in the luteal phase before ovarian stimulation increases clinical pregnancy rates in women with one or more previous implantation failures. DESIGN A nonblinded multicenter randomized clinical trial. SETTING Fertility clinics. PATIENT(S) Three hundred four eligible patients scheduled for IVF/intracytoplasmic sperm injection were randomized. The intervention group (n = 151) underwent endometrial scratching in the luteal phase before controlled ovarian stimulation, while no intervention was performed in the control group (n = 153). INTERVENTION(S) Endometrial scratching with a Pipelle de Cornier catheter in the luteal phase before ovarian stimulation. MAIN OUTCOME MEASURE(S) Clinical pregnancy rate and prenatal and birth data. RESULT(S) There was no overall significant improvement in clinical pregnancy rates between the control and intervention groups (38.5% vs. 44.4%; relative risk = 1.15; confidence interval [0.86-1.55]). However, subgroup analyses revealed that women with three or more previous implantation failures had a significant increase in clinical pregnancy rate (31.1% vs. 53.6%; relative risk = 1.72; confidence interval [1.05-2.83]) after scratching. No difference was seen as regards prenatal and birth data between the two groups. CONCLUSION(S) Endometrial scratching in the luteal phase before ovarian stimulation significantly enhances the clinical pregnancy rate in women with three or more prior implantation failures. This result seems to corroborate previous reports, which found that particularly women with repeated implantation failure seem to gain a positive effect from endometrial scratching. Importantly, there were no significant differences in prenatal data and birth data between the groups. CLINICAL TRIAL REGISTRATION NUMBER NCT01963819.