Puerto Rico offers a unique opportunity to collect longitudinal data on women at high risk of preterm births to explore relationships with environmental exposures because: (1) at 19.9%, Puerto Rico has the highest rate of preterm births of any jurisdiction in the US, (2) the rate of preterm birth has been increasing since 1995 and had not reached a plateau as of 2006, (3) preliminary data show that the observed increase is not explained by the traditional risk factors of preterm birth, including access to health care, tobacco exposure in pregnancy, maternal education, type of delivery, and maternal age, and (4) it has a high density of Superfund and national priority list sites within its 3500 square miles with well-documented contamination. Core C Human Subjects and Sampling (HSS) is designed to provide human subjects data and human and environmental specimens to four projects to facilitate much-needed research on demographic, environmental and genetic contributors to preterm birth. The University of Puerto Rico Medical Science Campus and the Graduate School of Public Health have the infrastructure and long-term experience in conducting clinical studies and population-based surveys in a culturally-sensitive manner, and will be the main site for coordination and execution of the recruitment, data and biological sample collection needed to support this program. Recruitment for the Core will take place at three hospitals in Puerto Rico's north coast with high rates of preterm birth (up to 41% of births) and their affiliated physician's clinics. A total of 1200 women will be recruited through the core during their second trimester, and detailed information on potential predictors of preterm birth, including medical and pregnancy history, demographic variables, self-reported environmental exposures, etc., will be collected through a research nurse-administered interview. Blood and urine samples, along with added exposure information, will be collected from the women at their 20-week and 28-week prenatal visits. At delivery, maternal blood and hair, cord blood, and placental tissue will be collected from a subset of women, and clinical data will be recorded for all births. All samples will be collected, processed and stored according to strict protocols. Samples will then be packaged and transferred to the various investigators and sites in regular batches to support the individual projects' research aims.