Residential Proximity to Oil and Gas Development and Birth Outcomes in California: A Retrospective Cohort Study of 2006-2015 Births

B ACKGROUND : Studies suggest associations between oil and gas development (OGD) and adverse birth outcomes, but few epidemiological studies of oil wells or inactive wells exist, and none in California. O BJECTIVE : Our study aimed to investigate the relationship between residential proximity to OGD and birth outcomes in California. M ETHODS : We conducted a retrospective cohort study of 2,918,089 births to mothers living within 10 km of at least one production well between January 1, 2006 and December 31, 2015. We estimated exposure during pregnancy to inactive wells count (no inactive wells, 1 well, 2 - 5 wells, 6+ wells) and production volume from active wells in barrels of oil equivalent (BOE) (no BOE, 1 - 100 BOE/day, 100 BOE / day). We used generalized estimating equations to examine associations between overall and trimester -speci fi c OGD exposures and term birth weight (tBW), low birth weight (LBW), preterm birth (PTB), and small for gestational age birth (SGA). We assessed e ff ect modi fi cation by urban/rural community type. R ESULTS : Adjusted models showed exposure to active OGD was associated with adverse birth outcomes in rural areas; e ff ect estimates in urban areas were close to null. In rural areas, increasing production volume was associated with stronger adverse e ff ect estimates. High (>100 BOE / day) vs. no production throughout pregnancy was associated with increased odds of LBW [odds ratio ? OR ? = 1 . 40, 95% con fi dence interval (CI): 1.14, 1.71] and SGA (OR =1 . 22, 95% CI: 1.02, 1.45), and decreased tBW (mean di ff erence = - 36 grams, 95% CI: - 54, - 17), but not with PTB (OR = 1 . 03, 95% CI: 0.91, 1.18). C ONCLUSION : Proximity to higher production OGD in California was associated with adverse birth outcomes among mothers residing in rural areas. Future studies are needed to con fi rm our fi ndings in other populations and improve exposure assessment measures. https://doi.org/10.1289/EHP5842