Time Series Evaluation of Birth Defects in Areas with and without Unconventional Natural Gas Development

Few studies have evaluated the association of unconventional natural gas development (UNGD) on birth defects and most of them neglect birth defects secular trend prior to UNGD and did not fully take into account maternal characteristics. We used 2003-2012 Pennsylvania birth registry data to assess the association between UNGD and birth defects using segmented regression analysis of interrupted time series method controlling for maternal characteristics and pre-drilling secular trend. Among areas with UNGD, birth defects prevalence rate was 6.3/1,000 live births before UNGD and 5.0/1,000 live births after UNGD, a 20.6% drop with P<0.01, while birth defects prevalence rate in zip code areas without UNGD was 4.7/1,000 live births. After controlling for maternal characteristics and secular trend, the adjusted odds ratio (aOR) for annual postUNGD birth defects trend did not change (aOR=1.00, P=0.29) and post-UNGD birth defects level decreased but was not statistically significant (aOR =0.97, P=0.12). The aOR for unconventional well number per square kilometer was 0.93, P=0.10. We conclude UNGD was not associated with birth defects prevalence rate trend and level changes. Further studies are needed to address why birth defects prevalence rate in UNGD areas were consistently 22% higher than in non-UNGD areas.