Risk of perinatal mortality associated with asthma during pregnancy: a 2-stage sampling cohort study.

BACKGROUND The association between maternal asthma during pregnancy and perinatal mortality has been investigated in 21 studies, and a significantly increased risk among asthmatic women was found in 4 studies. However, these studies have methodologic limitations, such as lack of adjustment for cigarette smoking, a major risk factor for perinatal mortality. OBJECTIVE To evaluate whether maternal asthma during pregnancy increases the risk of perinatal mortality. METHODS From the linkage of 3 administrative databases from Québec, Canada, a cohort including 13,100 asthmatic and 28,042 nonasthmatic women who had at least 1 pregnancy between 1990 and 2002 was constructed. We used a 2-stage sampling cohort design to obtain information on cigarette smoking and other potential confounders from the medical records of 1,247 selected mothers. RESULTS In the cohort, 353 cases of perinatal mortality were identified, and we were able to retrieve the medical record of the mother for 304 cases. A significantly increased crude risk of perinatal mortality of 34% among asthmatic women compared with nonasthmatic women was found, but the odds ratio did not remain significant after adjustment for placental abruption and cigarette smoking (odds ratio, 1.12; 95% confidence interval, 0.87-1.45). CONCLUSION The risk of perinatal mortality was not found to be significantly associated with maternal asthma after the effect of smoking was removed.