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. Author manuscript; available in PMC: 2018 Jul 6.
Published in final edited form as: Birth Defects Res A Clin Mol Teratol. 2010 Nov 15;91(1):29–33. doi: 10.1002/bdra.20743

Table 2.

Maternal Cigarette Smoking Exposures during the Periconceptional Period1 and Odds Ratios of Neural Tube Defects, National Birth Defects Prevention Study, 1997–2004

No. of cases No. of controls Crude ORs (95% CI) Adjusted2 ORs (95% CI)
Nonsmokers3 651 3940 1.0 (referent) 1.0 (referent)
Passive exposure only 218 814 1.6 (1.4–1.9) 1.7 (1.4–2.0)
Active cigarette smoking4 172 1108 0.9 (0.7–1.0) 0.9 (0.8–1.1)
 1–14 cigarettes/day 123 773 1.0 (0.8–1.2) 1.0 (0.8–1.3)
 15–24 cigarettes/day 36 277 0.8 (0.6–1.1) 0.9 (0.6–1.3)
 ≥25 cigarettes/day 13 58 1.4 (0.7–2.5) 1.6 (0.9–3.0)
1

The period from one month before to one month after conception.

2

Odds ratios were adjusted for race-ethnicity and center.

3

Nonsmokers who were not exposed to passive smoke.

4

Active cigarette smokers whether or not exposed to passive smoke.

OR, odd ratio; CI, confidence interval.