Research Article: Maternal residential proximity to unconventional gas development and perinatal outcomes among a diverse urban population in Texas

Date Published: July 21, 2017

Publisher: Public Library of Science

Author(s): Kristina W. Whitworth, Amanda K. Marshall, Elaine Symanski, Jaymie Meliker.


To assess associations between unconventional natural gas development (UGD) and perinatal outcomes.

We conducted a retrospective birth cohort study among 158,894 women with a birth or fetal death from November 30, 2010-November 29, 2012 in the Barnett Shale, in North Texas. We constructed three UGD-activity metrics by calculating the inverse distance-weighted sum of active wells within three separate geographic buffers surrounding the maternal residence: ≤½, 2, or 10-miles. We excluded women if the nearest well to her residence was >20 miles. Metrics were categorized by tertiles among women with ≥1 well within the respective buffer; women with zero wells ≤10 miles (the largest buffer) served as a common referent group. We used logistic or linear regression with generalized estimating equations to assess associations between UGD-activity and preterm birth, small-for-gestational age (SGA), fetal death, or birthweight. Adjusted models of fetal death and birthweight included: maternal age, race/ethnicity, education, pre-pregnancy body mass index, parity, smoking, adequacy of prenatal care, previous poor pregnancy outcome, and infant sex. Preterm birth models included all of the above except parity; SGA models included all of the above except previous poor pregnancy outcome.

We found increased adjusted odds of preterm birth associated with UGD-activity in the highest tertiles of the ½- (odds ratio (OR) = 1.14; 95% confidence interval 1.03, 1.25), 2- (1.14; 1.07, 1.22), and 10-mile (1.15; 1.08, 1.22) metrics. Increased adjusted odds of fetal death were found in the second tertile of the 2-mile metric (1.56; 1.16, 2.11) and the highest tertile of the 10-mile metric (1.34; 1.04–1.72). We found little indication of an association with SGA or term birthweight.

Our results are suggestive of an association between maternal residential proximity to UGD-activity and preterm birth and fetal death. Quantifying chemical and non-chemical stressors among residents near UGD should be prioritized.

Partial Text

Advancements in horizontal drilling and hydraulic fracturing have increased access to previously untapped natural gas reserves in shale formations. Unconventional natural gas development (UGD) is associated with several potential environmental hazards. The hydraulic fracturing process involves injecting a pressurized mixture of sand, water, and proprietary fracking fluid into wellbores, fracturing the rock and unlocking trapped hydrocarbons [1]. Fracking fluid may contain compounds that are known or possible human carcinogens, regulated under the Safe Drinking Water Act, or classified as hazardous air pollutants [2]. Ground and surface water contamination can occur from migration of fluids through failed well casings, leakage from open pit storage, and improper disposal or treatment of wastewater [3–7]. Further, many compounds found in fracking fluid and wastewater have been indicated for their reproductive or developmental toxicity [8, 9]. Multiple air pollutants including volatile organic compounds (VOCs) (e.g., toluene, benzene), polycyclic aromatic hydrocarbons (e.g., naphthalene, benzo(a)pyrene), nitrogen oxides, ozone, and particulate matter have also been detected near unconventional drilling sites [6, 10–14]. In addition to potential chemical exposures, individuals living in communities near UGD may experience noise and light pollution, noxious odors, and increased psychosocial stressors [15, 16]. Non-chemical stressors can contribute to allostatic load, reducing overall health and wellbeing [17], and potentially increase susceptibility to chemical stressors [18].

This retrospective birth cohort study included women with a singleton birth or fetal death from November 30, 2010-November 29, 2012 in the 24-county Barnett Shale area (Archer, Bosque, Clay, Comanche, Cooke, Coryell, Dallas, Denton, Eastland, Ellis, Erath, Hill, Hood, Jack, Johnson, Montague, Palo Pinto, Parker, Shackelford, Somervell, Stephens, Tarrant, Wise, and Young counties), in North Texas. Birth and fetal death records were obtained from the Texas Department of State Health Services (TXDSHS) for 166,966 births and 866 fetal deaths. This study was approved by the Committee for Protection of Human Subjects at The University of Texas Health Science Center at Houston and the TXDSHS IRB.

Fig 1 outlines the study process and exclusions. Briefly, through the process of cleaning gestational age [23–25], we excluded 28 (<1%) births missing both LMP- and clinical-based estimates of gestational age as well as 185 (<1%) births with estimated gestational age <22 or >44 completed weeks (Fig 1). A total of 227 births were excluded due to implausible/improbable gestational age estimates. We excluded five fetal deaths with no estimate of gestational age. Among records with a street-level geocode, 1,149 (<1%) were located outside the study area and were also excluded. An additional 5,764 (3.5%) subjects were excluded because the nearest UGD well was >20 miles from the residence. The final sample was 158,894: 158,104 live births and 790 fetal deaths.

We found evidence of a moderate positive association between maternal residential proximity to UGD-activity and increased odds of preterm birth and a suggestive association with fetal death. Not surprisingly, we found that the characterization of UGD was dependent upon the distance within which activity was defined.




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