Ambient Air Pollution and Stillbirths Risk in Sydney, Australia

Abstract

We aimed to determine the associations between ambient air pollution, specifically particulate matter less than or equal to 10 microns and 2.5 microns (PM10 and PM2.5 respectively) and ozone (O3), and stillbirths. We analysed all singleton births between 20–42 weeks gestation in metropolitan Sydney, Australia, from 1997 to 2012. We implemented logistic regression to assess the associations between air pollutants and stillbirth for each trimester and for the entire pregnancy. Over the study period, there were 967,694 live births and 4287 stillbirths. Mean levels of PM10, PM2.5 and O3 for the entire pregnancy were 17.9 µg/m3, 7.1 µg/m3 and 3.2 ppb, respectively. Adjusted odds ratios were generally greater than unity for associations between PM and stillbirths, but none were statistically significant. There were no significant associations between O3 and stillbirths. There was potential effect modification of the PM10 and O3 association by maternal age. We did not find consistent evidence of associations between PM and O3 and stillbirths in Sydney, Australia. More high quality birth cohort studies are required to clarify associations between air pollution and stillbirths.

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

“…Particles with slightly bigger sizes including PM 2.5-10 and PM 10 were also observed to be associated with stillbirth [28,37]. On the other hand, a number of studies from Texas and California, USA; Korea; Australia; and Iran showed no associations with particles of any sizes [28,31,39,40,44,47]. Constituents of fine particles were also investigated in two studies [31,43], one of which found that an interquartile range (0.007 μg/m 3 ) increase in average zinc particle exposure during the entire gestational period was associated with an 11% increased risk for stillbirth in Harris County, Texas [31].…”

“…Of the 14 studies evaluating the associations between PM 2.5 and stillbirth [28,31,34,36,37,[39][40][41][42][43][44][45][46][47], seven suggested positive association [34,36,37,[41][42][43]46], six suggested null association [28,31,39,40,44,47], and one showed inverse association [45]. Positive associations between stillbirth and whole-pregnancy average PM 2.5 exposures were observed in two large case-control analyses of pregnancies from three south Asian countries [41,42] and several large cohort studies in Southern Israel [46] and China [34,37].…”

“…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].…”

“…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].…”

“…Sixteen studies evaluated the associations between air pollutants and stillbirth during the review period (Table 2) [27,28,30,31,34,36,37,[39][40][41][42][43][44][45][46][47]. Like the case for spontaneous abortion discussed above, PM 2.5 , NO 2 , and O 3 received the most attention.…”