PROJECT SUMMARY Thousands of unplanned births occur at home in the US each year, and most trigger 911 emergency medical services (EMS) activations (i.e., calls for service). For these high-risk patients, evidence from other countries suggest unplanned out-of-hospital delivery (OHD) is associated with an increased risk of postpartum hemorrhage, neonatal hypothermia, neonatal intensive care unit admission, and maternal and neonatal death. However, little is known about the epidemiology and patient safety of OHD and other obstetric conditions treated by EMS personnel in the US. These major knowledge gaps have resulted in the lack of any evidence-based guidelines for EMS care of an obstetric patient and an ongoing lack of prehospital-specific training in this major area of maternal and child health. The overarching objective of this exploratory R21 project is to better understand the characteristics and clinical care of prehospital obstetric conditions treated by EMS personnel to inform future interventions that will reduce morbidity and mortality and improve prehospital patient care. We will use a national repository of EMS patient care records, the National Emergency Medical Services Information System (NEMSIS), to investigate prehospital care of mothers and their newborn infants. Collectively, from January 2018 to December 2019, NEMSIS includes >50 million EMS patient care records from 47 states and territories and over 10,000 EMS agencies, representing the largest sample of prehospital care records available. In Aim 1, we will describe the patient, community, emergency response, and clinical characteristics of OHDs and other high-risk obstetric conditions treated by EMS personnel, including examining differences by key factors like urbanicity, community-level racial distribution, and maternal age. In Aim 2, we will examine the frequency and prehospital factors associated with patient safety events during OHD and maternal and neonatal resuscitation. In Aim 3, we will use a modified Delphi method with a panel of 10-18 clinical and EMS experts to identify research priorities to improve prehospital care of obstetric conditions. Based on our pilot data, we estimate identifying approximately 7,000 EMS activations for OHD, with over 80% power for the statistical analyses in Aims 1 and 2. The present R21 project will provide a unique opportunity for the first national description of EMS care of obstetric patients in the US and prehospital-specific research priorities to guide research and interventions to improve prehospital patient outcomes and safety. This study directly responds to the NICHD priority to improve treatment of women at high risk for pregnancy-related morbidities and mortality; the Notice of Special Interest in Research on Emergency Medical Services for Children (NOT-HD-19-022); the Notice of Special Interest in Research in the Emergency Setting (NOT-NS-20-005); and the Healthy People 2030 objectives to reduce maternal deaths and severe m...