Table 1.
Population characteristics for the dataset used to establish the exposure–response curves between PM2.5 and stillbirth or other similar outcomes
| Variable | Group | Outcomes and their matched controls | |||
|---|---|---|---|---|---|
| Stillbirth | Early stillbirth | Miscarriage | Pregnancy loss | ||
| Categorical variables | Number (percentage) | ||||
| Total | 46,319 (100%) | 32,665 (100%) | 279,147 (100%) | 358,131 (100%) | |
| Pregnancy loss | Control | 32,449 (70.1%) | 22,882 (70.1%) | 193,599 (69.4%) | 248,930 (69.5%) |
| Case | 13,870 (29.9%) | 9,783 (29.9%) | 85,548 (30.6%) | 109,201 (30.5%) | |
| Number of matched controls | 1 | 10,162 (21.9%) | 6,864 (21.0%) | 61,494 (22.0%) | 78,520 (21.9%) |
| 2 | 11,556 (24.9%) | 8,400 (25.7%) | 78,573 (28.1%) | 98,529 (27.5%) | |
| 3 | 8,988 (19.4%) | 6,924 (21.2%) | 58,152 (20.8%) | 74,064 (20.7%) | |
| 4 | 7,015 (15.1%) | 4,930 (15.1%) | 38,315 (13.7%) | 50,260 (14.0%) | |
| 5+ | 8,598 (18.6%) | 5,547 (17.0%) | 42,613 (15.3%) | 56,758 (15.8%) | |
| Maternal age (years) | <20 | 9,712 (21.0%) | 7,081 (21.7%) | 51,841 (18.6%) | 68,634 (19.2%) |
| 20–29 | 25,699 (55.5%) | 17,548 (53.7%) | 157,077 (56.3%) | 200,324 (55.9%) | |
| 30–34 | 6,638 (14.3%) | 4,667 (14.3%) | 41,342 (14.8%) | 52,647 (14.7%) | |
| > 34 | 4,270 (9.2%) | 3,369 (10.3%) | 28,887 (10.3%) | 36,526 (10.2%) | |
| Level of nightlight (NTL, Digit-Number) | Low (NTL ≤ 4) | 29,464 (63.6%) | 18,947 (58.0%) | 130,672 (46.8%) | 179,083 (50.0%) |
| Middle (4 < NTL ≤ 20.5) | 10,310 (22.3%) | 7,585 (23.2%) | 73,896(26.5%) | 91,791 (25.6%) | |
| High (NTL > 20.5) | 6,545 (14.1%) | 6,133 (18.8%) | 74,579 (26.7%) | 87,257 (24.4%) | |
| Parity | Nulliparous | 13,175(28.4%) | 8,634 (26.4%) | 75,080 (26.9%) | 96,889 (27.1%) |
| Multiparous | 33,144 (71.6%) | 24,031 (73.6%) | 204,067 (73.1%) | 261,242 (72.9%) | |
| Continuous variable | Mean (Standard deviation, interquartile range) | ||||
| Maternal age (years) | Total | 25.45 (6.38, 20.58 ~ 29.58) | 25.56 (6.62, 20.50 ~ 29.83) | 25.90 (6.43, 21.00 ~ 30.00) | 25.81 (6.44, 20.92 ~ 29.92) |
| Control | 24.97 (6.02, 20.42 ~ 28.83) | 24.92 (6.23, 20.17 ~ 29.00) | 25.01 (5.99, 20.50 ~ 28.83) | 25.00 (6.02, 20.42 ~ 28.83) | |
| Case | 26.56 (7.02, 21.08 ~ 31.50) | 27.05 (7.22, 21.50 ~ 32.00) | 27.90 (6.92, 22.58 ~ 32.58) | 27.66 (6.98, 22.33 ~ 32.42) | |
| Temperature (°C) | Total | 23.67 (4.68, 21.48 ~ 26.76) | 23.63 (5.06, 21.26 ~ 26.84) | 23.20 (6.24, 20.16 ~ 27.14) | 23.30 (5.96, 20.49 ~ 27.03) |
| Control | 23.74 (4.70, 21.54 ~ 26.81) | 23.69 (5.09, 21.32 ~ 26.87) | 23.22 (6.23, 20.24 ~ 27.11) | 23.33 (5.95, 20.57 ~ 27.03) | |
| Case | 23.53 (4.64, 21.37 ~ 26.60) | 23.50 (4.99, 21.12 ~ 26.77) | 23.14 (6.26, 19.94 ~ 27.20) | 23.22 (5.97, 20.31 ~ 27.05) | |
| Nightlight (Digit-Number) | Total | 7.44 (15.35, 0.00 ~ 6.40) | 9.70 (17.51, 0.00 ~ 9.00) | 13.69 (20.12, 0.00 ~ 19.00) | 12.52 (19.47, 0.00 ~ 16.00) |
| Control | 7.07 (14.99, 0.00 ~ 5.75) | 9.11 (17.01, 0.00 ~ 8.33) | 12.93 (19.67, 0.00 ~ 17.00) | 11.81 (19.01, 0.00 ~ 14.00) | |
| Case | 8.29 (16.14, 0.00 ~ 7.20) | 11.06 (18.54, 0.00 ~ 12.00) | 15.42 (21.01, 0.00 ~ 25.00) | 14.12 (20.40, 0.00 ~ 21.00) | |
| PM2.5 (µg/m3) | Total | 40.53 (22.46, 24.40 ~ 49.65) | 38.37 (24.53, 22.01 ~ 46.40) | 40.01 (29.54, 21.20 ~ 48.20) | 39.93 (28.30, 21.65 ~ 48.20) |
| Control | 40.34 (22.20, 24.41 ~ 49.38) | 38.07 (24.01, 22.07 ~ 46.22) | 39.57 (29.25, 21.00 ~ 47.70) | 39.53 (27.98, 21.53 ~ 47.78) | |
| Case | 40.96 (23.04, 24.35 ~ 50.22) | 39.07 (25.69, 21.87 ~ 46.89) | 41.01 (30.17, 21.57 ~ 49.27) | 40.83 (28.98, 21.92 ~ 49.17) | |