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.