The extent to which childhood asthma incidence is influenced by asthma control and severity during pregnancy is unknown. We have studied this association during the child's first 10 yrs of life.

A two-stage, case–control study, nested in a cohort of 8,226 children of asthmatic mothers, was conducted using three interlinked databases of Quebec, Canada, and mailed questionnaires. A total of 2,681 asthmatic children and 30,318 age-matched controls were selected (≤20 controls·case⁻¹; stage 1), and 3,254 selected mothers were mailed questionnaires to obtain additional information (stage 2). Asthma control and severity was defined using validated indexes and childhood asthma incidence based on at least one asthma-related diagnosis and prescription received within 2 yrs. A total of 44 confounders were considered.

Compared with children of mild controlled asthmatic mothers, children whose mothers had moderate-to-severe uncontrolled asthma during pregnancy had an increased risk of asthma (adjusted OR 1.27, 95% CI 1.06–1.52). No increased risk was observed for children of mild uncontrolled and moderate-to-severe controlled mothers.

Based on one of the largest studies of children of asthmatic mothers, a significant increase in asthma risk was demonstrated among children whose mothers had poor control and increased severity of asthma during pregnancy, indicating that this element should be added to the expanding list of determinants of childhood asthma. As it constitutes a risk factor where pregnant asthmatic females can intervene, it is of great importance for physicians to optimally treat asthmatic females during pregnancy and to encourage females to be adherent to the prescribed asthma medications.