1. In a large cohort comparing 35,000 pregnancies of women living near hydraulic fracturing sites to unexposed controls in rural Alberta, Canada, exposure was associated with increased risk of small for gestational age (SGA) and major congenital anomalies.
2. Residential proximity to a greater number of well sites was associated with increased risks of SGA and spontaneous preterm birth.
Evidence Rating Level: 2 (Good)
Study Rundown: Hydraulic fracturing, or “fracking,” for the extraction of oil and natural gas has been associated with potential detrimental effects on public health, including birth outcomes, in nearby areas, though the issue remains understudied. This study aimed to examine the association between maternal geographic proximity to hydraulic fracturing wells and outcomes such as preterm birth and small for gestational age (SGA) birth in rural Alberta, Canada. A cohort of about 9,200 pregnancies of women living near active well sites either during pregnancy or in the year before conception was compared with a control group including 26,000 pregnancies of women living more than 10 kilometers from a site. Exposure to an active well was associated with a 12% higher risk of SGA status and a 31% higher risk of major congenital anomalies. Women living within 10 kilometers of more than 100 wells had increased risk of spontaneous preterm birth and SGA compared to those living near 1-24 wells. In a sensitivity analysis, exposure both before conception and during pregnancy was associated with increased risks, but exposure during either period alone was not. This study shows that within a single rural region, proximity to active hydraulic fracturing is associated with modest increases in risk for adverse birth outcomes. These effects are likely to be indirect, via factors like groundwater contamination or air pollution associated with extraction. Further research is needed to determine how best to protect patients in affected areas, but this work adds to data indicating that currently widespread energy extraction methods are detrimental to human as well as environmental health.
Click to read the study in JAMA Pediatrics
Relevant Reading: A review of the public health impacts of unconventional natural gas development
In-Depth [retrospective cohort]: Information about hydraulic fracturing well locations and timing of extraction was drawn from a government database. Exposure was defined as distance of 10 kilometers or less from at least 1 site active during preconception or pregnancy. Statistical analysis adjusted for demographic factors including parental age at birth, multiple births, infant sex, comorbidities, and socioeconomic status. Only mothers aged 18-50 living within postal codes classified as rural were included. Well site exposure was associated with an adjusted risk ratio (ARR) of 1.12, with a 95% confidence interval (CI) of 1.03-1.23, for SGA and 1.31 (1.01-1.69) for major congenital anomalies. There was no association between distance to the nearest well site and any adverse birth outcomes. Exposure during the third trimester alone was significantly associated with SGA (ARR 1.18, 95% CI 1.05-1.33) compared to unexposed controls, while second trimester exposure was associated with severe neonatal morbidity or mortality (1.25, 1.03-1.52).
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