Time-Varying Exposure to Ozone and Risk of Stillbirth in a Nonattainment Urban Region

Abstract

In a racially and ethnically diverse urban area (Harris County, Texas) with historic nonattainment O3 levels, we obtained birth and fetal death records from 2008–2013 and estimated maternal residential O3 concentrations from conception until delivery using inverse-distance interpolation from the local air monitoring network. We examined multipollutant models (with fine particulate matter and nitrogen dioxide) and effect measure modification by race/ethnicity and length of gestation. We found a 9% (95% confidence interval (CI): 1, 18) increased stillbirth risk associated with a 3.6-parts-per-billion increase in O3 exposure. The risk was higher among women with pregnancies of <37 gestational weeks (hazard ratio (HR) = 1.13, 95% CI: 1.04, 1.23) compared with women with pregnancies of longer gestation (HR = 1.05, 95% CI: 0.87, 1.27) and among Hispanic women (HR = 1.14, 95% CI: 1.02, 1.27). We also conducted a case-crossover analysis and detected no associations with short-term exposure. To our knowledge, this study is the first to use time-to-event analyses to examine stillbirth risk associated with time-varying prenatal ozone (O3) exposure over pregnancy. Our findings indicate that maternal O3 exposure over pregnancy is associated with stillbirth risk and that Hispanic women and women with shorter pregnancies might be at particular risk.

Outdoor Air Pollution and Pregnancy Loss: a Review of Recent Literature

“…The majority of the studies included in this review were conducted in the USA (n = 6, 28.6%) [27][28][29][30][31][32] and China (n = 6, 28.6%) [33][34][35][36][37][38], followed by Iran (n = 2, 9.5%) [39,40], South Asia (n = 2, 9.5%) [41,42], Africa (n = 1, 4.8%) [43], Australia (n = 1, 4.8%) [44], England (n = 1, 4.8%) [45], Israel (n = 1, 4.8%) [46], and Korea (n = 1, 4.8%) [47]. Retrospective cohort (n = 6) [31,34,[44][45][46][47] and case-control designs (n = 6) [30,35,38,[41][42][43] were most popular, followed by times series (n = 3) [33,39,40], prospective cohort (n = 2) [27,37], and case-crossover designs (n = 2) [28,32]. Two studies also used multiple designs to ensure robustness of findings [29,36].…”

“…Two studies also used multiple designs to ensure robustness of findings [29,36]. Most studies (n = 12) [27,29,31,32,36,38,[41][42][43][45][46][47] assessed exposures using the modeling approaches, while the rest used measurements from fixed-site air monitors (n = 9) [28, 30, 33-35, 37, 39, 40, 44]. In terms of exposure, 12 studies assessed long-term exposures across different periods of pregnancy [30, 34-38, 41, 42, 44-47], five studies assessed short-term impacts of exposures within the last week [28,32,33,39,40], three studies assessed both short-and long-term impacts [27,31,43], and one study investigated average exposure in the study area with no specific window [29].…”

“…Most studies (n = 12) [27,29,31,32,36,38,[41][42][43][45][46][47] assessed exposures using the modeling approaches, while the rest used measurements from fixed-site air monitors (n = 9) [28, 30, 33-35, 37, 39, 40, 44]. In terms of exposure, 12 studies assessed long-term exposures across different periods of pregnancy [30, 34-38, 41, 42, 44-47], five studies assessed short-term impacts of exposures within the last week [28,32,33,39,40], three studies assessed both short-and long-term impacts [27,31,43], and one study investigated average exposure in the study area with no specific window [29]. In terms of study outcome, 10 studies investigated stillbirth [28,30,31,34,37,40,[44][45][46][47], five studies assessed spontaneous abortion [29,32,33,35,38], four studies evaluated both pregnancy loss outcomes [39,[41][42][43], and two studies evaluated any loss without categorization based on gestational age…”

“…In terms of exposure, 12 studies assessed long-term exposures across different periods of pregnancy [30, 34-38, 41, 42, 44-47], five studies assessed short-term impacts of exposures within the last week [28,32,33,39,40], three studies assessed both short-and long-term impacts [27,31,43], and one study investigated average exposure in the study area with no specific window [29]. In terms of study outcome, 10 studies investigated stillbirth [28,30,31,34,37,40,[44][45][46][47], five studies assessed spontaneous abortion [29,32,33,35,38], four studies evaluated both pregnancy loss outcomes [39,[41][42][43], and two studies evaluated any loss without categorization based on gestational age [27,36]. One study measured pregnancy loss prospectively using clinical assessment [27], five used questionnaires [29,36,[41][42][43], and 15 relied on administrative data or medical records [28, 30-35, 37-40, 44-47].…”

Sex and Gender Differences in the Susceptibility to Environmental Exposures

“…Pregnant women have also been reported to be more susceptible to ozone exposure, which can result in premature delivery and complications of pregnancy such as low birth weight, preterm birth, and stillbirth (Bekkar et al 2020;Zang et al 2019;Díaz et al 2016). These effects appear to be time-dependent and more severe in women in the third trimester of pregnancy (Rammah et al 2019;Grippo et al 2018;Mendola et al 2017).…”