Unconventional Gas Development Activity and Severity of Preterm Birth in the Barnett Shale, TX

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Background: Studies of the relation between maternal residential proximity to unconventional gas development (UGD) and preterm birth (PTB) are equivocal. No study has presented specific risk estimates by UGD-phase or pregnancy trimester.Methods: We conducted a case-control study among women with singleton births in the Barnett Shale area, TX, November 30, 2010–November 29, 2012. Five controls were individually matched to each PTB case (n=13,328) on age and race/ethnicity and controls’ time-at-risk was truncated to equal the matched case’s gestational age. We created separate activity metrics representing two phases of UGD for wells ≤½ mile of the maternal residence. The inverse distance-weighted (IDW) count of wells in the drilling phase represented the UGD-drilling metric and the IDW sum of gas produced represented the UGD-production metric. Metrics were created for each trimester and the entire pregnancy and categorized as: zero wells (ref), 1st, 2nd, and 3rd tertiles of UGD-activity. Conditional logistic regression was used to examine associations with PTB and multinomial logistic regression was used to examine associations with PTB severity, classified as extreme, very, or moderate PTB.Results: We found increased odds of PTB among women classified in the third tertiles of the UGD drilling (1.2, 1.1-1.4) and production (1.2, 1.1-1.3) metrics. Among women classified in the highest tertile of the UGD production metric, the strongest association was observed during the first trimester (1.2, 1.0-1.4). Risk estimates for the UGD-drilling metric were similar across trimesters. We noted the greatest risk for extremely PTB [third tertile ORs: UGD drilling, 2.0 (1.2, 3.2); UGD production, 1.5 (1.0-2.3)].Conclusion: Our results suggest differences in phase- and trimester-specific association between UGD and PTB, and indicate particular risk associated with extremely PTB.