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Table 1 Descriptive characteristics of the study sample

From: Association between metal cobalt exposure and the risk of congenital heart defect occurrence in offspring: a multi-hospital case-control study

Variable

Control, n = 490 (%)

Cases, n= 399 (%)

Chi square

P value

Maternal age (years, n) a

  

7.803

0.099

n < 20

12 (2.4)

12 (3.0)

  

 20 ≤ n < 25

111 (22.7)

113 (28.3)

  

 25 ≤ n < 30

216 (44.1)

179 (44.9)

  

 30 ≤ n< 35

108 (22.0)

73 (18.3)

  

n ≥ 35

43 (8.8)

22 (5.5)

  

Gestational age (week, n) a

  

37.628

< 0.001***

n < 15

6 (1.2)

2 (0.5)

  

 15 ≤ n< 20

69 (14.1)

15 (3.8)

  

 20 ≤ n < 25

233 (47.6)

182 (45.6)

  

 26 ≤ n<31

109 (22.2)

136 (34.1)

  

n ≥ 31

73 (14.9)

64 (16.0)

  

Folic acid supplement

  

11.350

0.001**

 Yes

436 (89.0)

323 (81.0)

  

 No

54 (11.0)

76 (19.0)

  

Parental smoking

  

15.615

< 0.001***

 Yes

181 (36.9)

200 (50.1)

  

 No

309 (63.1)

199 (49.9)

  

ppBMI (kg/cm2)

  

3.987

0.136

 BMI < 18.5

120 (23.1)

116 (27.6)

  

 18.5 ≤ BMI< 25

381 (73.3)

295 (70.2)

  

 BMI ≥ 25

19 (3.7)

9 (2.1)

  

mEDU

  

38.113

< 0.001***

 Primary school and below

3 (0.6)

16 (4.0)

  

 Junior middle school

77 (15.7)

114 (28.6)

  

 Senior high school

124 (25.3)

89 (22.3)

  

 College degree and above

284 (58.0)

173 (43.4)

  
  1. aUsing base data in following multivariate analysis as continuous variables
  2. **P < 0.01, ***P < 0.001, two-tailed test, there was statistically significant difference between groups