Extending the Environmental influences on Child Health Outcomes (ECHO) Cohort through 2030: Rationale and study protocol.

Early life environmental exposures, even those experienced before conception, can shape health and disease trajectories across the lifespan. Optimizing the detection of the constellation of exposure effects on a broad range of child health outcomes across development requires considerable sample size, transdisciplinary expertise, and developmentally sensitive and dimensional measurement. To address this, the National Institutes of Health (NIH) Environmental influences on Child Health Outcomes (ECHO) Cohort Study is an observational longitudinal pediatric cohort study. In the first phase from 2016-2023, the ECHO Program built a robust platform for investigating prenatal and early life environmental exposures on child health outcomes. Now, the ECHO Program is extending longitudinal follow-up of existing ECHO participants <21 years of age and recruiting and following new pregnant participants <20 weeks gestation and their offspring through 2030. Participants will be enrolled at 72 Cohort Study Sites across all 50 US states, the District of Columbia, and Puerto Rico. Exposure assessments span the biological, chemical/physical, lifestyle, and social environment; child health outcomes focus on five broad domains: pre-, peri-, postnatal; airways; obesity; neurodevelopment; and positive health, or one's physical, mental, and social well-being. Data and biospecimens will be collected annually through August 2030, with an expected total sample size of 60,000 children and their caregivers. The ECHO Cohort Study represents the largest national longitudinal study of children's health in the US. Here, we describe the ECHO Cohort "Cycle 2" observational study arm and the ECHO Cohort Protocol version 3.0 (ECP v3.0), which delineates the data elements, measures, and biospecimens that all ECHO Cycle 2 Cohort Study Sites will collect and analyze.