CDC conducts national pregnancy-related mortality surveillance to better understand the risk factors for and causes of pregnancy-related deaths in the United States. The Pregnancy Mortality Surveillance System (PMSS) defines a pregnancy-related death as a death while pregnant or within 1 year of the end of pregnancy from any cause related to or aggravated by the pregnancy. Medical epidemiologists review and analyze death records, linked birth records and fetal death records if applicable, and additional available data from all 50 states, New York City, and Washington, DC. PMSS is used to calculate the pregnancy-related mortality ratio, an estimate of the number of pregnancy-related deaths for every 100,000 live births. The birth data used to calculate pregnancy-related mortality ratios were obtained from the National Vital Statistics System (NVSS) via the Centers for Disease Control and Prevention, Wide-ranging Online Data for Epidemiologic Research (CDC WONDER).