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 live 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 12) 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.