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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)  
  1. aNumber of participants; b Data are number (percentage). Total number may not be equal to the number of cases or controls due to missing or unknown data; c Pearson’s χ2 test, or Fisher's exact test if cell expectation was less than 5.or Fisher's exact test if cell expectation was less than 5; d Kruskal-Wallis test; e Mann-Whitney U test