ABSTRACT Pregnant women are exposed daily to multiple chemical and non-chemical stressors, including air pollutants, phthalates, and psychosocial stress. The Developmental Origins of Health and Disease model (DOHaD) states that exposure to these stressors in pregnancy affects fetal development in a manner that impacts offspring health across the life course. Yet epidemiologic data in these areas is limited, particularly with U.S. samples. It is also poorly understood whether these exposures prenatally affect childhood neurodevelopment and airway health in an independent or combined manner, and likely moderators of effects, such as the sex of the child, are infrequently addressed. We propose to unify three diverse extant pregnancy cohorts?TIDES (N=717, 2010-12), GAPPS (N=1133, 2012-16), and CANDLE (N=1385, 2007-11), for a combined sample size of 3235 mother-child dyads in the PATHWAYS study. PATHWAYS will investigate how chemical (air pollutants and phthalates) and non-chemical (psychosocial stress) exposures during pregnancy are related to placental gene expression (transcriptome) and childhood neurodevelopment and airway health (at ages 4-6, 8-9, and 10-11 years). Each cohort has rich resources of prenatal data and banked specimens (urine, blood, and placenta) that will be harmonized for the PATHWAYS study and will contribute to the ECHO consortium. We will develop a national model with high spatiotemporal resolution of key air pollutants and assess urinary markers of maternal exposure. A composite measure will capture multilevel maternal psychosocial stress across pregnancy, and urinary phthalate and blood stress hormone (CRH) levels in the second and third trimesters will provide individual assessment of those exposures in potential critical periods. We will characterize the placental transcriptome using RNA sequencing and will assess neurodevelopment and airway health prospectively into middle childhood. PATHWAYS will examine how these prenatal exposures are related to the placental transcriptome and child health outcomes in main effect and interactive models, with emphasis on sex-specific associations. For both neurodevelopment and airway health, we propose to measure both phenotypic precursors of health outcomes (i.e. fluid cognition, lung function growth), which yield dimensional tests of proposed associations, as well as clinically meaningful and policy relevant outcomes (i.e. asthma, mental health). Our study is powered to assess interactive effects of chemical and non-chemical stressors and will be the first study to characterize how prenatal environmental exposures relate to placental transcriptome pathways in relation to childhood health outcomes. This represents a significant scientific advance in testing DOHaD hypotheses. Major contributions to the ECHO Consortium include: 1) the development of a state of the art national model of air pollution, 2) a large, diverse pregnancy cohort with extensive biorepositories and extant prenatal and postnatal biomarkers, placental transcriptome, psychosocial and environmental data, and 3) an experienced, interdisciplinary team that will contribute meaningfully to the ECHO program of work.