This study aims to examine the effects of low-level exposures to prevalent neurotoxicants on health, growth, and neurobehavior among a representative sample of children. Pregnant women were enrolled in the project around 16 weeks of gestation. In the first phase of the study, we followed children resulting from the pregnancy through the age of 36 months. The second phase extended follow-up through 72 months. Phase 3 extended follow-up to 8 years (range 7.5-10) with comprehensive neurobehavioral assessments. Phase 4 will allow follow-up at 12 years (range 11-13), and includes measures of health, growth and body composition, behavior and mental health, and neuroimaging. To address the potential adverse health risks of environmental chemicals, including persistent pollutants such as PBDEs and PFCs and other non-persistent chemicals, on fetal, infant, and child neurobehavior, the investigators are systematically examining their associations with endocrine function, cognition, learning and memory, motor skills, attention and executive function, and behavior from age 1 to 7.5-10 years. The investigators are also examining exposures at different developmental stages (in utero at 16 weeks of gestation, early childhood, school age, preadolescence) using stored biological samples and measure child neurobehavior at 1, 2, 3, 4, 5, 8, and 12 years. This longitudinal study will allow the investigators to determine the dose response, windows of susceptibility, and persistence of the association. The investigators are also examining the contribution of PBDE exposures from house dust in a subset of children who have complete sets of samples of maternal serum and child serum collected from annual visits along with extensive measures of mouthing behaviors.