Table 1.

Demographic Characteristics as Percent of Subjects between 1997 and 2006 in Eight Counties in the San Joaquin Valley of California (N = 1723)

	Percent of casesa (n=874)	Percent of controlsa (n=849)	p Value of chi-square test
Maternal education (years)			0.20
<12	36	32
12	25	27
>12	38	40
Missing	<1	<1
Maternal race/ethnicity			0.36
White	29	31
Foreign-born Hispanic	33	29
U.S.- born Hispanic	26	26
Other	12	14
Missing	<1	<1
Multi-vitamin useb			0.08
Yes	61	65
No	37	33
Missing	2	2
Smokingc			0.41
None	75	75
Active only	7	8
Passive only	12	10
Active and passive	6	6
Missing	1	<1
Maternal age (years)			0.32
<25	42	46
25–35	47	44
>35	11	10
Infant sex			0.01
Male	58	52
Female	42	48
Missing	<1	0
Plurality			<0.01
Singletons	95	99
Multiples	5	1
Parity			0.51
0	40	38
1	29	31
>1	31	32
Year of expected delivery date			0.12
1997–2000	33	37
2001–2003	32	33
2004–2006	35	31

^aPercentages may not equal 100 owing to rounding.

^bAny folate-containing multi-vitamin use during 1 month before through 2 months after conception.

^cAny smoking during 1 month before through 2 months after conception.