Passive smoking is associated with poor asthma control during pregnancy: a prospective study of 500 pregnancies

Asthma and tobacco exposure is common among pregnant women. We investigated the effect of passive and active smoking on asthma control during pregnancy.

Prospective observational design. Patients had their asthma control, based on symptoms, use of medication, spirometry, and exhaled nitric oxide [FENO], assessed every four weeks during 2nd and 3rd trimester of pregnancy; data on tobacco exposure were also collected prospectively. The primary outcome was episodes of uncontrolled and partly controlled asthma during pregnancy (defined according to GINA-guidelines).

A total of 500 pregnant women with asthma (mean age 30.8 years, range 17 to 44) were consecutively included, of whom 32 (6.4%), 115 (23.0%) and 353 (70.6%), respectively, were current smokers, ex-smokers and never smokers [NS]. Sixty-five NS (18.4%) reported passive tobacco exposure. NS with passive tobacco exposure had significantly lower FEV1% predicted (p<0.02) and FENO (p = 0.01) compared to NS without passive tobacco exposure. The relative risk [RR] of an episode of uncontrolled asthma during pregnancy was 4.5 (95% CI 2.7-7.5: p<0.001) in current and ex-smokers compared with never smokers, and 2.9 (95% CI 1.4-5.9; p = 0.004) in NS-women with passive tobacco exposure compared with NS-women not reporting passive tobacco exposure. Treatment with inhaled corticosteroids, most likely as a marker of more severe asthma, was also associated with a higher risk (RR 8.1, 95% CI 5.1-13.0; p<0.001) of an episode of uncontrolled asthma.

Passive tobacco exposure in never smokers is associated with an increased risk of episodes of uncontrolled asthma during pregnancy, which is likely to have adverse effects on pregnancy outcome.