TABLE 1.
Characteristics of controls and cases in Liaoning Province, China, 2010–2015 [no.(%)] (Association between maternal exposure to SO2 and congenital ear malformations in offspring: a population-based case-control study in Liaoning Province, China, 2010–2015).
| Characteristics | Cases | Controls | p-Value |
|---|---|---|---|
| Total | 1676 (100) | 7950 (100) | |
| Season of conception | <0.001 | ||
| Spring | 443 (26.4) | 2106 (26.5) | |
| Summer | 444 (26.5) | 2829 (35.6) | |
| Fall | 440 (26.3) | 1705 (21.4) | |
| Winter | 349 (20.8) | 1310 (16.5) | |
| Gender of infant | <0.001 | ||
| Female | 720 (43.0) | 3927 (49.4) | |
| Male | 956 (57.0) | 4023 (50.6) | |
| Gestational age, weeks | <0.001 | ||
| <37 | 102 (6.1) | 257 (3.2) | |
| ≥37 | 1574 (93.9) | 7693 (96.8) | |
| Birth weight, grams | <0.001 | ||
| <2500 | 89 (5.3) | 174 (2.2) | |
| 2500–<4000 | 1410 (84.1) | 6840 (86.0) | |
| ≥4000 | 177 (10.6) | 936 (11.8) | |
| Maternal age, years | <0.001 | ||
| <30 | 1080 (64.4) | 4704 (59.2) | |
| ≥30 | 596 (35.6) | 3246 (40.8) | |
| Gravidity | <0.001 | ||
| 1 | 918 (54.8) | 5026 (63.2) | |
| ≥2 | 758 (45.2) | 2924 (36.8) | |
| Parity | <0.001 | ||
| 1 | 1348 (80.4) | 7695 (96.8) | |
| ≥2 | 328 (19.6) | 255 (3.2) | |
| Maternal education | <0.001 | ||
| Elementary school or less | 68 (4.1) | 265 (3.3) | |
| Middle school | 659 (39.3) | 2912 (36.6) | |
| High school | 394 (23.5) | 1723 (21.7) | |
| College or above | 555 (33.1) | 3050 (38.4) |