PM_2.5 threshold exceedances during the prenatal period and risk of intellectual disability

Background: Research demonstrates that chronic exposure to fine particulates (PM2.5) increases risks of neurodevelopmental conditions, such as intellectual disability (ID). Few studies have examined neurodevelopmental health impacts of pollution spikes exceeding 24-h (24-h) PM2.5 guidelines, despite relevance to the regulatory landscape. The current potential for regulatory changes to 24-h PM2.5 standards in the United States makes research on exceedances relevant. Objective: To examine associations between 24-h PM2.5 exceedances and the risk of ID. Methods: We conducted a retrospective case-control study of a sample of children in Utah, USA. We used generalized estimating equations to predict odds of ID based on the number of 24-h PM2.5 exceedance days during the preconception period and three trimesters of pregnancy. Exceedance days are defined as per current World Health Organization (WHO) [>= 15 mu g/m(3)] and current US Environmental Protection Agency (EPA) [>= 35 mu g/m(3)] 24-h guidelines. Results: PM2.5 exceedances are associated with ID risk during the preconception and first trimester periods and not the second and third trimesters. During the preconception period, each day exceeding 15 mu g/m(3) or 35 mu g/m(3) was associated with a 1.023 (CI: 1.011-1.040) or 1.042 (CI: 1.026-1.059, p < 0.001) increase in odds of ID, respectively. During the first trimester, each day exceeding 15 mu g/m(3) or 35 mu g/m(3) was associated with a 1.032 (CI: 1.017-1.047) or 1.059 (CI: 1.030-1.088) increase in odds of ID, respectively.