# Community Water Fluoridation and Birth Outcomes

## TL;DR

A study of over 11 million births found no link between community water fluoridation and adverse birth outcomes like low birth weight.

## Contribution

This study provides rigorous causal evidence that community water fluoridation is not associated with negative birth outcomes.

## Key findings

- No statistically significant changes in birth weight were observed following the introduction of community water fluoridation.
- Event-study estimates showed no significant changes in birth outcomes across all posttreatment periods.
- Sensitivity analyses confirmed the robustness of the findings, supporting the safety of CWF during pregnancy.

## Abstract

Is community water fluoridation (CWF) associated with changes in birth weight among infants born before and after its introduction in US counties?

In this cohort study of 11 479 922 singleton births across 677 counties between 1968 and 1988, aggregated to the county-month level, CWF was not associated with statistically significant changes in birth weight.

These findings suggest that concerns about changes in birth weight associated with CWF may be unfounded, underscoring the value of rigorous research designs in evaluating potential adverse effects from CWF.

This cohort study evaluates the association between prenatal exposure to community water fluoridation and birth weight and other birth outcomes in US counties.

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.

To evaluate the association between prenatal exposure to CWF and birth outcomes.

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.

County-level CWF.

The primary outcome was change in mean birth weight, and secondary outcomes were incidence of low birth weight (<2500 g), gestational length (weeks), and incidence of prematurity (gestational age <37 weeks). Community water fluoridation exposure was measured as the population-weighted share of county residents served by fluoridated water based on Centers for Disease Control and Prevention Fluoridation Census data.

The study sample included 11 479 922 singleton births (mean [SD] gestational age, 39.5 [0.8] weeks; 51.2% boys; mean [SD] birth weight, 3337.4 [172.8] g; highest mean [SD] maternal age proportions, 0.36 [0.13] aged 20-24 years and 0.27 [0.12] aged 25-29 years) across 677 counties (408 CWF treated [60.3%] and 269 [39.7%] never treated) over the 21-year period, aggregated to the county-month level. No evidence of an association of CWF with birth weight or other birth outcomes was found (DID estimate, −0.53; 95% CI, −4.75 to 3.70). Event-study estimates showed no discernible pretreatment trends and no significant changes following CWF adoption, with estimates small in magnitude across all posttreatment periods, ranging from −8.44 g (95% CI, −20.41 to 3.53 g) to 7.20 g (95% CI, −5.45 to 19.85 g). Findings were supported by sensitivity analyses incorporating state-specific time trends, alternative exposure thresholds, and tests for compositional changes in births.

This cohort study of more than 11 million births found no association of CWF with adverse birth outcomes. These findings provide reassurance about the safety of CWF during pregnancy and underscore the value of rigorous causal designs in evaluating potential adverse effects of public health interventions.