Table 1 Baseline characteristics of participants between case group and control group

Maternal age, n (%)

28.24 ± 5.02

29.00 ± 4.27

< 0.001^a

Maternal BMI

20.73 ± 2.54

20.41 ± 2.04

0.016 ^a

Education, n (%)

 Primary school and below

8 (1.36)

5 (0.42)

< 0.001

 Junior middle school

27 (4.60)

111 (9.41)

 High middle school

227 (38.67)

147 (12.46)

 Above high middle school

325 (55.37)

917 (77.71)

Ethnicity, n (%)

 Han

572 (97.44)

1172 (99.32)

0.001

 Other

15 (2.56)

8 (0.68)

Residence, n (%)

 Rural

390 (66.44)

391 (33.14)

< 0.001

 Urban

197 (33.56)

789 (66.86)

Family wealth index, n (%)

 Low

309 (52.64)

325 (27.54)

< 0.001

 Medium

161 (27.43)

391 (33.14)

 High

117 (19.93)

464 (39.32)

Parity, n (%)

 0

360 (61.33)

947 (80.25)

< 0.001

 1

200 (34.07)

223 (18.90)

 ≥ 2

27 (4.60)

10 (0.85)

Abortion history, n (%)

 Yes

206 (35.09)

425 (36.02)

0.703

 No

381 (64.91)

755 (63.98)

Family history of birth defects, n (%)

 Yes

58 (9.88)

61 (5.17)

< 0.001

 No

529 (90.12)

1119 (94.83)

Active or passive smoking, n (%)

 Yes

345 (58.77)

678 (57.46)

< 0.001

 No

242 (41.23)

502 (42.54)

Drinking, n (%)

 Yes

18 (3.07)

8 (0.68)

< 0.001

 No

569 (96.93)

1172 (99.32)

Folic acid supplement, n (%)

 Yes

450 (76.66)

1020 (86.44)

< 0.001

 No

137 (23.34)

160 (13.56)

Fever, n (%)

 Yes

53 (9.03)

78 (6.61)

0.068

 No

534 (90.97)

1102 (93.39)

Taking medicine, n (%)

 Yes

129 (21.98)

161 (13.64)

< 0.001

 No

458 (78.02)

1019 (86.36)

GDM, n (%)

 Yes

16 (2.73)

44 (3.73)

0.273

 No

571 (97.27)

1136 (96.27)

TORCH infections, n (%)

 Yes

6 (1.02)

2 (0.17)

0.032 ^b

 No

581 (98.98)

1178 (99.83)

Industries exposure, n (%)

 Yes

73 (12.44)

42 (3.56)

< 0.001

 No

514 (87.56)

1138 (96.44)