Methods: This study examined the impact of proximity to fracking across the US on birth outcomes overall and by race/ethnicity. We used 2005-2018 county-level natality files on 33,994,423 singletons from 28 states linked with monthly production levels, defined as the sum of the inverse-distance-squared weighted production of natural gas from wells per county averaged across 9 months prior to birth. We conducted difference-in-differences linear regression models for birth weight (grams) adjusted for women’s demographic characteristics, prenatal smoking, gestational age, and year, with county fixed effects; subsequently, we included an interaction between weighted production and race/ethnicity. We also conducted binomial probit models for binary outcomes of low birth weight and small-for-gestational age with the similar model specifications, including county random effects. We report semi-elasticities computed from average marginal effects.
Results: While the number of counties with fracking declined from 964 to 900 between 2005 and 2018, gas production increased over this time by 69%. We found that a 10% increase in gas production decreased birth weight by 3.24 grams (95% CI -4.97 to -1.51). A significant interaction (p<0.001) revealed that reductions in birth weight were greater for infants born to Black (-12.75 grams), Asian (-3.93 grams) and Hispanic (-2.55 grams) women, than infants born to white women (-1.85 grams). Furthermore, a 10% increase in gas production increased infants born low birth weight by 0.007 percentage points (95% CI 0.005 to 0.009) and small-for-gestational age by 0.023 percentage points (95% CI 0.020 to 0.027) (both p<0.001). Significant interactions revealed similarly higher risk of adverse birth outcomes among infants born to Black, Asian, and Hispanic women than infants born to white women.
Conclusions and Implications: Prenatal exposures to higher volumes of gas production from fracking were associated with poorer birth outcomes, particularly among infants born to Black women. Our findings indicate that the effects of fracking on pregnancy extend beyond single localities to affect infants born in all states with fracking.