Table 1 Characteristics and hair thorium concentrations (Conc., unit: ng/g hair) of the recruited mothers who had pregnancies affected by total neural tube defects (Cases), those who delivered healthy infant (Controls), and the total population (Total)
From: Thorium and fetal neural tube defects: an epidemiological evidence from large case-control study
Group | Controls (N = 511) a | Cases (N = 263) | Total (N = 774) | P c | Hair thorium Conc. in Total group (N = 774) | P |
|---|---|---|---|---|---|---|
Age (y) | ||||||
 < 25 | 233 (45.8) b | 118 (45.0) | 351 (45.5) | 0.510 | 0.68 (0.38–1.06) | < 0.001 d |
 25–29 | 157 (30.8) | 75 (28.6) | 232 (30.1) |  | 0.56 (0.32–1.01) |  |
 30–34 | 95 (18.7) | 50 (19.1) | 145 (18.8) |  | 0.99 (0.61–1.55) |  |
 > 34 | 24 (4.7) | 19 (7.3) | 43 (5.6) |  | 1.18 (0.79–1.96) |  |
Education | ||||||
 Primary school or lower | 39 (7.6) | 44 (16.8) | 83 (10.7) | < 0.001 | 1.09 (0.70–1.80) | < 0.001 d |
 Junior high school | 311 (60.9) | 176 (67.2) | 487 (63.0) |  | 0.81 (0.50–1.26) |  |
 High school | 107 (20.9) | 34 (13.0) | 141 (18.2) |  | 0.40 (0.25–0.69) |  |
 College or higher | 54 (10.6) | 8 (3.1) | 62 (8.0) |  | 0.36 (0.21–0.55) |  |
Previous birth defects history | ||||||
 No | 501 (98.8) | 236 (91.1) | 737 (96.2) | < 0.001 | 0.71 (0.40–1.18) | < 0.001 e |
 Yes | 6 (1.2) | 23 (8.9) | 29 (3.8) |  | 0.88 (0.57–1.56) |  |
Occupation | ||||||
 Non-chemical industry worker | 492 (97.2) | 225 (94.1) | 717 (96.2) | 0.062 | 0.70 (0.40–1.18) | < 0.001 e |
 Chemical industry worker | 14 (2.8) | 14 (5.9) | 28 (3.8) |  | 0.78 (0.36–1.27) |  |
Fever or influenza during early pregnancy | ||||||
 No | 487 (97.0) | 202 (78.9) | 689 (90.9) | < 0.001 | 0.69 (0.38–1.16) | < 0.001 e |
 Yes | 15 (3.0) | 54 (21.1) | 69 (9.1) |  | 0.99 (0.66–1.46) |  |
Periconceptional folic acid supplementation | ||||||
 No | 341 (69.0) | 206 (81.1) | 547 (73.1) | 0.001 | 0.80 (0.45–1.30) | < 0.001 e |
 Yes | 153 (31.0) | 48 (18.9) | 201 (26.9) |  | 0.49 (0.26–0.82) |  |
Passive smoking | ||||||
 No | 354 (69.5) | 161 (61.2) | 515 (66.7) | 0.025 | 0.70 (0.39–1.16) | < 0.001 e |
 Yes | 155 (30.5) | 102 (38.8) | 257 (33.3) |  | 0.78 (0.43–1.23) |  |
Gravidity | ||||||
 1 | 224 (44.0) | 116 (44.4) | 340 (44.2) | 0.961 | 0.66 (0.38–1.05) | < 0.001 d |
 2 | 200 (39.3) | 100 (38.3) | 300 (39.0) |  | 0.78 (0.41–1.23) |  |
 3+ | 85 (16.7) | 45 (17.2) | 130 (16.9) |  | 0.89 (0.45–1.42) |  |
Cooking frequency | ||||||
 Rarely | 256 (53.2) | 109 (41.8) | 365 (49.2) | 0.004 | 0.59 (0.33–0.96) | < 0.001 e |
 Frequently | 225 (46.8) | 152 (58.2) | 377 (50.8) |  | 0.88 (0.48–1.42) |  |
Main fuel type for cooking | ||||||
 Not coal | 303 (59.9) | 85 (32.4) | 388 (50.5) | < 0.001 | 0.48 (0.28–0.75) | < 0.001 e |
 Coal | 203 (40.1) | 177 (67.6) | 380 (49.5) |  | 1.02 (0.69–1.61) |  |