Table 3. Association between periconceptional passive smoking and risk for fetal NTDs subtypes in five counties, Shanxi Province, China, 2010–2016.

Groups	Number	Number of passive smoking exposure	Crude OR (95% CI)	Adjusted OR* (95% CI)
*Adjusted for maternal age, prepregnancy BMI, education, fever or flu in early pregnancy, nausea and vomiting during pregnancy (NVP), periconception folic acid use and history of birth defect-affected pregnancy. Abbreviations: NTDs=neural tube defects; OR=odds ratio; CI=confidence interval; BMI=body mass index.
Control	523	154	1.0	1.0
Anencephaly	78	42	2.795 (1.724−4.532)	2.497 (1.433−4.352)
Spina bifida	121	78	4.346 (2.864−6.596)	3.907 (2.404−6.348)
Encephaloceles	25	13	2.596 (1.158−5.817)	2.540 (1.043−6.188)