Community Water Fluoridation and Birth Outcomes

Importance: Community water fluoridation (CWF) is a widely implemented public health intervention aimed at preventing dental caries. However, concerns have emerged about potential unintended birth outcomes of fluoride exposure, particularly birth weight, which is a widely accepted summary measure of infant health and has been found to be associated with later-life health and human capital. Objective: To evaluate the association between prenatal exposure to CWF and birth outcomes. Design, Setting, and Participants: This cohort study was conducted using an event-study analysis with a difference-in-differences (DID) approach that exploited the staggered rollout of CWF across US counties from January 1968 to December 1988. The study included birth outcomes from singleton births obtained from the National Vital Statistics System's Natality Detail Files. The analysis compared within-county changes in birth outcomes before and after the introduction of CWF, using counties that never fluoridated or had not yet fluoridated as the control. Data were analyzed between February 4 and October 28, 2025. Exposure: County-level CWF. Main Outcomes and Measures: The primary outcome was change in mean birth weight, and secondary outcomes were incidence of low birth weight (