PROJECT SUMMARY/ABSTRACT Stillbirth, fetal death occurring at least 20 weeks’ gestation, is one of the most common adverse pregnancy outcomes, affecting over 3 million pregnancies per year worldwide. Stillbirth leads to substantial economic and emotional burden on affected families and the health care system. Women experiencing stillbirth are at increased risk of its recurrence and other obstetric complications in subsequent pregnancies. Though an etiology may be found in some couples, stillbirth is unexplained in about 50% of cases. Sadly, emotional ordeals for families are exacerbated by widespread misconceptions about unexplained stillbirths, such as it being a rare occurrence, and by increased feelings of self-blame and guilt. Apart from infrequent aneuploidies, underlying causal genetic factors of unexplained cases are largely unknown. Recently, we showed that stillbirth aggregates in families, suggesting that investigating genes in high-risk familial stillbirth pedigrees will reveal important insights into pathogenic heritable genes. Additionally, by whole- exome sequencing (WES) of maternal-offspring dyads, we identified small genetic abnormalities that were previously impossible to ascertain.However, the results from our WES analysis pose many challenges for interpretation and identification of pathogenic variants affecting regulatory elements or a large and diverse set of genes. Whole genome sequencing (WGS) analysis of DNA from both parents, stillbirths, and live births, offers the opportunity to comprehensively detect a complete set of genetic abnormalities (e.g., single- nucleotide polymorphisms, insertion/deletions, and structural variants, including the rest of the genome that are biochemically active). In a pilot WGS study using DNA from parents, unexplained recurrent fetal death including stillbirths, and live births, we showed that inherited and newly occurring, i.e., de novo variants may be relevant to fetal death. With a larger WGS study and novel shared risk variants analyses in pedigrees, we can identify inherited and de novo variants as causal and contributory factors for stillbirth. The findings will lead to improved risk stratification and discovery of novel pathophysiologic pathways and therapeutic targets. Therefore, we propose the following Specific Aims: Aim 1) Identify novel inherited variants relevant to familial and recurrent stillbirth, Aim 2) Identify de novo variants that are part of the ‘intolerome’ and relevant to sporadic stillbirth. We will conduct WGS analysis using DNA from both parents and their offspring (stillbirths and live births). The scientific aims of this study are complemented and enhanced by the proposed team’s overall commitment and expertise in the field of reproductive medicine and in stillbirth genetic research as well as existing IRB-approved data and samples. Our study will have a significant impact by providing an explanation for stillbirth, facilitating bereavement and emotional closure...