Association between residential proximity to hydraulically fractured oil and gas wells and adverse birth outcomes in California (2006-2015)

Abstract

BACKGROUND AND AIM: Hydraulic fracturing (HF) is a chemically intensive oil and gas extraction method. Although studies indicate exposure to HF during pregnancy may be associated with adverse birth outcomes, no health studies on HF exposure have been conducted in California. METHODS: We conducted a retrospective cohort study of 979,961 births to mothers in eight California counties with HF wells between 2006-2015 to assess the relationship between prenatal exposure to HF wells and adverse birth outcomes. Exposed individuals were those that had at least 1 HF well within 1 km of their residence throughout their pregnancy and the reference population had no wells within 1 km but at least one oil or gas well within 10 km. We used generalized estimating equations to examine associations between HF well exposure and low birth weight (LBW), preterm birth (PTB), small for gestational age birth (SGA), and term birth weight (tBW). We assessed effect modification by urban/rural communities using stratified models. RESULTS:Less than one percent of mothers (N=1,192) were exposed to HF during pregnancy. Among rural mothers, prenatal HF exposure was associated with 74% increased odds of LBW (odds ratio [OR] = 1.74 and 95% confidence interval [CI]: 1.10, 2.75), 68% increased odds of SGA (OR = 1.68, 95% CI: 1.42, 2.27), 73 grams lower tBW (mean difference: -73 g, 95% CI: -131, -15) and 17% increased odds of PTB (OR = 1.17, 95% CI: 0.64, 2.12). Among urban mothers, we observed a positive association between HF exposure and SGA (OR = 1.23, 95% CI: 0.98, 1.55) and inverse associations with LBW (OR: 0.83, 95% CI: 0.63, 1.07) and PTB (OR: 0.65, 95% CI: 0.48, 0.87). CONCLUSIONS:Proximity to HF was associated with adverse birth outcomes among rural women in California. Future research is needed to better characterize specific hazards associated with HF. KEYWORDS: birth outcomes, oil and gas development, hydraulic fracturing, pregnancy exposure