Abstract Background Exposure to unconventional hydraulically fractured oil and gas wells during pregnancy is associated with a higher risk of structural birth defects. These associations have not been examined in California, where most operators use conventional methods that do not use enhanced techniques. Objectives Determine whether residing near oil and gas wells during early pregnancy was associated with birth defect risks among San Joaquin Valley, California, residents. Methods We conducted a case-control study with data from the California Center of the National Birth Defects Prevention Study for births delivered from 1997–2011. We considered 16 structural birth defect phenotypes. We assessed exposure to active wells within 3 km of the maternal residence or inactive wells within 1 km. We fit adjusted logistic regression models for each exposure and birth defect phenotype. Results Exposure to active wells was associated with elevated odds of some CHDs and significantly lower odds of atrial septal defect secundum and gastroschisis. Exposure to inactive wells was associated with significantly elevated odds of cleft palate. Conclusions Among San Joaquin Valley residents, living near active and inactive wells was associated with risks of birth defects. The estimates were imprecise and, given the number of statistical tests we conducted, may be spurious. Impact Researchers have not yet characterized structural birth defect-related potential risks associated with living near conventional wells in California, and there is little understanding of the hazards associated with inactive wells. We found that living near active wells in the San Joaquin Valley, California, was associated with risk of some structural birth defects, but findings were imprecise. Living near inactive wells was associated with an elevated risk of cleft lip and cleft palate. Further research could help determine whether findings were valid and explicate plausible etiological pathways.
Stone et al. (2026) studied this question.