Drilling and Production Activity Related to Unconventional Gas Development and Severity of Preterm Birth.

BACKGROUND Studies of unconventional gas development (UGD) and preterm birth (PTB) have not presented risk estimates by well development phase or trimester. OBJECTIVE We examined phase and trimester-specific associations between UGD activity and PTB. METHODS We conducted a case-control study of women with singleton births in the Barnett Shale area, Texas, from 30 November 2010 to 29 November 2012. We individually age- and race/ethnicity-matched five controls to each PTB case (n=13,328) and truncated controls' time at risk according to the matched case's gestational age. We created phase-specific UGD-activity metrics: a) inverse squared distance-weighted (IDW) count of wells in the drilling phase ≤0.5 mi (804.7 meters) of the residence and b) IDW sum of natural gas produced ≤0.5 mi of the residence. We also constructed trimester- and gestation-specific metrics. Metrics were categorized as follows: zero wells (reference), first, second, third tertiles of UGD activity. Analyses were repeated by PTB severity: extreme, very, and moderate (<28, 28 to<32, and 32 to<37 completed weeks). Data were analyzed using conditional logistic regression. RESULTS We found increased odds of PTB in the third tertile of the UGD drilling {odds ratio (OR)=1.20 [95% confidence interval (CI): 1.06, 1.37]} and UGD-production [OR=1.15 (1.05, 1.26)] metrics. Among women in the third tertile of UGD-production, associations were strongest in trimesters one [OR=1.18 (1.02, 1.37)] and two [OR=1.14 (0.99, 1.31). The greatest risk was observed for extremely PTB [third tertile ORs: UGD drilling, 2.00 (1.23, 3.24); UGD production, 1.53 (1.03-2.27)]. CONCLUSIONS We found evidence of differences in phase- and trimester-specific associations of UGD and PTB and indication of particular risk associated with extremely preterm birth. Future studies should focus on quantifying specific chemical and nonchemical stressors associated with UGD. https://doi.org/10.1289/EHP2622.