The Effect of Active and Passive Household Cigarette Smoke Exposure on Pregnant Women with Asthma

CHEST. 2010;137(3):601-608. 

In This Article

Abstract and Introduction


Background: The article was designed to estimate the effect of active and passive household cigarette smoke exposure on asthma severity and obstetric and neonatal outcomes in pregnant women with asthma.
Methods: We used a secondary observational analysis of pregnant women with mild and moderate-severe asthma enrolled in a prospective observational cohort study of asthma in pregnancy and a randomized clinical trial (RCT) comparing inhaled beclomethasone and oral theophylline. A baseline questionnaire detailing smoking history and passive household smoke exposure was given to each patient. Smoking status was confirmed in the RCT using cotinine levels. Data on asthma severity and obstetric and neonatal outcomes were collected and analyzed with respect to self-reported tobacco smoke exposure. Kruskal-Wallis and Pearson χ2 statistics were used to test for significance.
Results: A total of 2,210 women were enrolled: 1,812 in the observational study and 398 in the RCT. Four hundred and eight (18%) women reported current active smoking. Of the nonsmokers, 790 (36%) women reported passive household smoke exposure. Active smoking was associated with more total symptomatic days (P < .001) and nights of sleep disturbance (P < .001). Among the newborns of active smokers, there was a greater risk of small for gestational age < 10th percentile (P < .001), and a lower mean birth weight (P < .001). There were no differences in symptom exacerbation or outcome between nonsmokers with and without passive household cigarette smoke exposure.
Conclusions: Among pregnant women with asthma, active but not passive smoking is associated with increased asthma symptoms and fetal growth abnormalities.


Asthma is a common medical complication of pregnancy, affecting 6% to 8% of women.[1,2] Both the prevalence and morbidity of asthma are increasing in the general population.[3] The literature has been inconsistent regarding the relationship between asthma and adverse pregnancy outcomes. Increased risks of low birth weight (LBW), small for gestational age (SGA), and preterm delivery have been reported with asthma.[4–8] Larger studies, however, have identified fewer significant adverse obstetric outcomes.[1,9,10]

A multicenter prospective observational cohort study performed by the Maternal-Fetal Medicine Units Network evaluated the relationship between asthma severity and maternal and fetal morbidity among pregnant women with asthma and matched controls.[11] This study demonstrated a strong relationship between asthma severity and exacerbation during pregnancy, as well as associations with nonpulmonary pregnancy outcomes, including cesarean delivery, preeclampsia, gestational diabetes, and preterm birth.[12] Oral corticosteroid use was also associated with an increased incidence of preterm birth and LBW, but not SGA.[13]

Cigarette smoking is known to aggravate asthma.[14] Smoking is independently associated with both prematurity and intrauterine growth restriction,[15,16] as well as fetal and neonatal mortality.[17,18] A review of US national linked birth and infant death data for the 1997 birth cohort reported a prevalence of maternal smoking of 13.2%. The incidence of neonatal death was 40% higher among smokers, even after adjusting for confounding demographic variables.[19] The effect of cigarette smoking on perinatal outcome is also dose dependent. Neonatal mortality associated with smoking increased from 22% to 68% between the lowest and highest exposure groups.[19] The impact of smoking on pregnancy is usually underestimated, as maternal history underreports this exposure.[12]

Much less is known regarding the effect of passive environmental tobacco smoke (ETS) exposure on obstetric outcomes. Studies of ETS have revealed relatively modest effects on birth weight and length.[20,21] There are few data available regarding the effects of ETS exposure on pregnant patients with a hyperresponsive respiratory disorder such as asthma. The goal of this investigation was to determine the effect of active and passive household ETS exposure on asthma severity and obstetric and neonatal outcomes in women with asthma.


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