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The potential benefit of endometrial scratching (ES) on embryo implantation is still a controversial subject. At present, the single retrospective study in egg donor IVF cycles concluded that ES has no beneficial effect. Our objective was to determine if there are differences in clinical pregnancy rates (CPR) in egg donor cycles when an ES is performed. This is a randomized controlled trial (RCT) in egg donor IVF patients conducted at ProcreaTec Fertility Center in Madrid. Three hundred fifty-two patients were included in total. One hundred sixty-one patients completed the protocol in group A and 172 patients in group B. Patients allocated to group A received an ES in the luteal phase of the cycle preceding the embryo transfer cycle. Group B patients did not receive any intervention. Primary outcome of this RCT was CPR. Secondary outcomes were implantation (IR), miscarriage (MR), ongoing pregnancy (OPR), multiple pregnancy (MulPR), and live birth rates (LBR). CPR was 104 of 161 (64.6%) in group A and 102 of 172 (59.3%) in group B (RR 1.09, 95% confidence interval (CI) (0.92-1.29); p = 0.378). OPR, MR, MulPR, and LBR were also comparable. No major complications were detected after ES and pregnancy complications were comparable. Our results show that there is no beneficial role of ES in egg donor IVF cycles, considering these patients as the ideal model as they share homogeneous embryo quality and endometrial preparation protocols. This trial was registered on April 5, 2017, as the ENDOSCRATCH trial (NCT03108157).

Background Previous evidence indicates associations between the female reproductive tract microbiome composition and reproductive outcome in infertile patients undergoing assisted reproduction. We aimed to determine whether the endometrial microbiota composition is associated with reproductive outcomes of live birth, biochemical pregnancy, clinical miscarriage or no pregnancy. Methods Here, we present a multicentre prospective observational study using 16S rRNA gene sequencing to analyse endometrial fluid and biopsy samples before embryo transfer in a cohort of 342 infertile patients asymptomatic for infection undergoing assisted reproductive treatments. Results A dysbiotic endometrial microbiota profile composed of Atopobium, Bifidobacterium, Chryseobacterium, Gardnerella, Haemophilus, Klebsiella, Neisseria, Staphylococcus and Streptococcus was associated with unsuccessful outcomes. In contrast, Lactobacillus was consistently enriched in patients with live birth outcomes. Conclusions Our findings indicate that endometrial microbiota composition before embryo transfer is a useful biomarker to predict reproductive outcome, offering an opportunity to further improve diagnosis and treatment strategies.