Table 1.

Selected Maternal Characteristics of Neural Tube Defect Cases and Controls in the National Birth Defects Prevention Study, 1997–2005

Characteristic	Cases (n = 1,223)		Controls (n = 6,807)
	No.	%	No.	%
Race/ethnicity*
Non-Hispanic white	621	50.8	4,026	59.1
Non-Hispanic black	114	9.3	771	11.3
Hispanic	395	32.3	1,502	22.1
Asian/Pacific Islander	25	2.0	200	2.9
Other	64	5.2	279	4.1
Missing	4	0.3	29	0.4
Educational level, years*
<9	98	8.0	330	4.8
9–11	159	13.0	800	11.8
12	347	28.4	1,652	24.3
13–15	338	27.6	1,806	26.5
>15	265	21.7	2,110	31.0
Missing	16	1.3	109	1.6
Age at delivery, years*
<18	49	4.0	255	3.7
18–19	99	8.1	478	7.0
20–24	270	22.1	1,552	22.8
25–29	390	31.9	1,807	26.5
30–34	257	21.0	1,759	25.8
35–39	115	9.4	816	12.0
40–44	40	3.3	128	1.9
>44	3	0.2	12	0.2
Study center location*
Arkansas	153	12.5	848	12.5
California	240	19.6	858	12.6
Georgia	148	12.1	735	10.8
Iowa	146	11.9	759	11.2
Massachusetts	74	6.1	859	12.6
North Carolina	70	5.7	412	6.1
New Jersey	70	5.7	574	8.4
New York	72	5.9	601	8.8
Texas	171	14.0	792	11.6
Utah	79	6.5	369	5.4
Body mass index*,a
<18.5	49	4.0	361	5.3
18.5–24.9	576	47.1	3,640	53.5
25.0–29.9	254	20.8	1,463	21.5
>29.9	265	21.7	1,055	15.5
Missing	79	6.5	288	4.2
Folic acid supplement use
No	574	46.9	3,121	45.9
Yesb	605	49.5	3,521	51.7
Missing	44	3.6	165	2.4
Dietary folate equivalents, μgc
<331.73	320	26.7	1,636	24.6
331.73–491.13	306	25.6	1,682	25.3
491.14–722.40	278	23.2	1,688	25.4
>722.40	293	24.5	1,639	24.7

* P < 0.05 (cases vs. controls; subjects with complete data only).

^aWeight (kg)/height (m)².

^bRefers to any use in the period 1 month before conception through 1 month after conception.

^cQuartiles are based on control women’s distributions in dietary folate equivalents, and data are restricted to women with daily energy intakes of 500–5,000 kcal. Dietary folate equivalents were calculated as food folate intake + (1.7 × synthetic folic acid intake).