Previous studies have linked premature birth and other health problems with living near hydraulic fracturing, or fracking wells. This study, led by researchers at the March of Dimes Prematurity Center at Stanford University, focused on the San Joaquin Valley because most most oil and gas wells in California use conventional extraction methods (though some are fracking wells).
The study focused on spontaneous preterm births, meaning those that happen at least three weeks before the mother's due date for no known medical cause. Researchers examined 225,000 births from healthy mothers who lived within six miles of oil and gas wells in the San Joaquin Valley between 1998 and 2011. They found that women who lived near wells in their first and second trimesters were 8%-14% more likely to experience a spontaneous preterm birth, especially women who were non-white and/or didn't go to college, even after the researchers controlled for outside factors that could impact the health of such groups.
A secondary data analysis from Stanford's School of Earth, Energy & Environmental Sciences found a possible explanation for the preterm births: residents living near oil and gas wells may be exposed to more air pollution.