PM2.5 metal constituent exposure and stillbirth risk in Harris County, Texas

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].…”

“…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.…”

“…A few studies estimated exposures by linking residential address of participants (at the time of delivery) to local fixed air monitors [28,30,33,34,37,39,40,44]. This strategy assumes that people have the same exposure levels as measured at local fixed station(s), regardless of proximity.…”

“…For administrative data, different jurisdictions may be mandated to capture loss/mortality outcomes for births beyond different gestational age. As such while some studies defined stillbirth as death ≥ 20 weeks [28,30,31,34,44], others use different cutoffs including 22 weeks [40], 24 weeks [45,46], 28 weeks [37], and 5 months [41][42][43]. For miscarriage/spontaneous abortion, the range of definition included < 20 weeks [29,32,35], and < 13 weeks [38], and < 5 months [41][42][43].…”