Objective To determine whether spouses who only smoke cigarettes outside the home can reduce the secondhand smoke (SHS) exposure of non-smoking pregnant women to the levels of those with non-smoking spouses.

Methods In this cross-sectional survey performed between 1 October 2006 and 31 July 2007, 896 non-smoking pregnant women in their 35th gestational week were included. Hair nicotine levels and the smoking behaviour of their spouses at home were assessed.

Results The geometric means of the hair nicotine levels of the participants with non-smoking spouses (group A), the participants with spouses who only smoked outside the home (group B), and the participants with spouses who smoked inside the home (group C) were 0.33 ng/mg (95% CI 0.30 to 0.35), 0.51 ng/mg (95% CI, 0.45 to 0.57) and 0.58 ng/mg (95% CI, 0.51 to 0.65), respectively. The mean log hair nicotine level of group A was significantly different from the other groups (p<0.001, Scheffe's post hoc test). Multiple linear regression analysis of the log-transformed hair nicotine levels of the participants after adjusting for confounding showed that the mean differences (SE of the mean difference) of groups B and C compared to the reference group A were 0.43 (0.07; p<0.001) and 0.44 (0.10; p<0.001), respectively.

Conclusions Spouses who only smoked outside the home did not reduce the level of SHS exposure of pregnant women to the level of pregnant women with non-smoking spouses. A strategy based on the separation of pregnant women and the smoking activity of their spouses might be inadequate to protect pregnant women from SHS at home.