Table 1

Distribution of selected child and maternal characteristics and exposures for analysis of NTDs, NBDPS, 1997–2011

Characteristic or exposureIndividuals, No. (%)*
Controls
(n=10 409)
All NTDs
(n=1644)
Child characteristic
Sex
 Male5309 (51.1)760 (49.0)
 Female5089 (48.9)792 (51.0)
 Missing1192
First-degree family history of NTDs
 Yes17 (0.2)21 (1.3)
 No10 392 (99.8)1623 (98.7)
 Missing00
Study site
 Arkansas1282 (12.3)197 (12.0)
 California1136 (10.9)323 (19.6)
 Georgia1098 (10.5)207 (12.6)
 Iowa1149 (11.0)191 (11.6)
 Massachusetts1248 (12.0)85 (5.2)
 New Jersey501 (4.8)43 (2.6)
 New York874 (8.4)83 (5.0)
 North Carolina894 (8.6)164 (10.0)
 Texas1221 (11.7)203 (12.3)
 Utah1006 (9.7)148 (9.0)
 Missing00
Maternal characteristic
Race/ethnicity
 Non-Hispanic white5969 (57.4)840 (51.1)
 Non-Hispanic black1143 (11.0)142 (8.6)
 Hispanic2614 (25.1)561 (34.1)
 Other676 (6.5)101 (6.1)
 Missing70
Age at delivery (years)
 <253449 (33.1)535 (32.5)
 25–345528 (53.1)885 (53.8)
 ≥351432 (13.8)224 (13.6)
 Missing00
Educational level at delivery (years)
 <121736 (17.2)319 (19.9)
 12–155067 (50.2)873 (54.6)
 ≥163298 (32.7)407 (25.5)
 Missing30845
Prepregnancy BMI (kg/m2)
 <18.5549 (5.5)56 (3.7)
 18.5–24.95359 (54.1)735 (48.3)
 25.0–29.92240 (22.6)357 (23.5)
 ≥30.01752 (17.7)373 (24.5)
 Missing509123
Maternal exposure
Hypertension†
 Yes918 (8.9)126 (7.7)
 No9404 (91.1)1503 (92.3)
 Missing8715
Cigarette smoking‡
 No active or passive7153 (70.7)1102 (68.8)
 Active only772 (7.6)104 (6.5)
 Passive only1199 (11.9)265 (16.5)
 Active and passive987 (9.8)131 (8.2)
 Missing29842
Alcohol consumption‡
 Yes3551 (35.1)490 (30.6)
 No6557 (64.9)1111 (69.4)
 Missing30143
Fever‡
 Yes493 (5.1)116 (7.8)
 No9126 (94.9)1378 (92.2)
 Missing790150
Use of a supplement containing folic acid‡
 Yes5500 (54.2)848 (53.3)
 No4643 (45.8)743 (46.7)
 Missing26653
  • *Percentages within each column may not total 100 due to rounding.

  • †Diagnosed before or during pregnancy.

  • ‡One month before pregnancy through the first month of pregnancy.

  • BMI, body mass index; NBDPS, National Birth Defects Prevention Study; NTDs, neural tube defects.