ABSTRACT Pregnancy loss is the most common complication of human gestation, occurring in roughly one-half of natural conceptions and most frequently in the first two to three weeks of gestation. In recent years it has become apparent that constitutive endometrial dysfunction represents an important contributor to infertility in women being treated with assisted reproductive technologies (ART). This application is specifically focused on the endometrial origins and basis of embryo implantation failure (EIF), early pregnancy failure (EPF), and recurrent pregnancy loss (RPL) in ART patients. The central hypothesis is that idiopathic infertility primarily stems from constitutive endometrial dysfunction, attributable to defects in progesterone responsiveness of the endometrial epithelium and stroma as well as immune cells. The goal of this research is to begin testing this hypothesis by focusing on infertile women experiencing the continuum of first trimester pregnancy loss. A team of exceptional extramural and intramural investigators with complementary and substantial expertise in basic reproductive biology and translational reproductive sciences will address that hypothesis by conducting a collaborative research project. At the NIH Clinical Center, the endometrium from cohorts of normal healthy fertile donors and infertile patients with carefully phenotyped and clinically-defined EIF, EPL or RPL will be biopsied in an outpatient setting (Aim 1). Advanced single cell technologies will be used to interrogate the endometrium (Aim 1). Organoids will be used to functionally study progesterone responses of the endometrial epithelium (Aim 2). In vitro decidualization will be used to functionally interrogate hormone responsiveness and decidualization capacity of the endometrial stroma and understand the influence of decidual immune cells (Aim 3). Cutting- edge genomic and transcriptomic technologies and advanced bioinformatics and data integration will be used to understand cell type heterogeneity, cell-specific differences in gene expression, and discern critical progesterone-driven biological pathways important for endometrial function that are disrupted in infertile women. The proposed aims are conceptually and technically innovative and together will have a broad impact on the field by filling a substantial gap in our fundamental knowledge of uterine biology and infertility. This application specifically targets NIH funding opportunity announcement PAR-18-951 entitled “Opportunities for Collaborative Research at the NIH Clinical Center” and focuses on major research priorities of the Fertility and Infertility Branch of the NICHD. These efforts will contribute to our understanding of the cellular basis of idiopathic infertility, enable the development of new tests enabling clinicians to diagnose and prescribe regimens directed at treating specific underlying endometrial dysfunction, and ultimately impact pregnancy outcomes in assisted and natural conceptions enabled by a personalized medicine approach.

Public Health Relevance Early pregnancy loss is the most common complication of human pregnancy, and women with endometriosis are at risk for higher rates of early pregnancy loss. Recurrent implantation failure and pregnancy loss in women may involve defects in uterine receptivity for embryo implantation and pregnancy establishment that stem from dysfunction of the epithelium, stroma, and/or immune cells of the endometrium. This fundamental work will generate knowledge that can be translated to improve reproductive outcomes of natural and assisted pregnancies and understand the origins of common gynecological and reproductive disorders in women.