Table 1. Characteristics of the subject women in the case and control groups.

	Case group		Control group
Characteristics	Number	%	Number	% (%)	OR (95%CI)	P
Age (years)
≤24	75	16.3	90	19.6	1.000
24~28	161	35.1	176	38.3	1.109(0.752,1.636)	0.603
>28	223	48.6	193	42.1	1.397(0.964,2.027)	0.078
Occupation
Manual work	406	88.5	364	79.3	2.355(1.547,3.585)	<0.001
Brain work	53	11.6	95	20.7	1.000
Education level
≤Middle school	417	90.9	358	78.0	3.034(1.994,4.617)	<0.001
>Middle school	42	9.2	101	22.0	1.000
Annual income (RMB)
Low (≤12000)	299	65.1	189	41.2	3.245(2.356,4.47)	<0.001
High (>12000)	160	34.9	270	58.8	1.000
BMI*(kg/m2)
≤24	340	74.1	370	80.6	1.000
>24	119	25.9	89	19.4	1.484(1.075,2.048)	0.016
Passive smoking
Yes	177	38.6	78	17.0	3.750(2.596,5.416)	<0.001
No	282	61.4	381	83.0	1.000
Exposure to pesticide
Yes	32	7.0	6	1.3	6.196(2.41,15.93)	<0.001
No	427	93.0	453	98.7	1.000
Intake of folic acid supplements
Yes	142	30.9	230	50.1	0.429(0.321,0.572)	<0.001
No	317	69.1	229	49.9	1.000
Maternal chronic diseases
Yes	30	6.5	14	3.1	2.332(1.186,4.586)	0.014
No	429	93.5	445	96.9	1.000