Asthma exacerbations and inhaled corticosteroid use in pregnancy and child asthma

<bold>Background:</bold> Among pregnant women with asthma, maternal exacerbations increase the risk of child asthma whilst taking inhaled corticosteroids (ICS) during pregnancy may decrease the risk. We used two population-wide register-based cohorts with family designs to assess these relationships. <bold>Methods:</bold> Study populations- mothers with asthma and children born: 1) 2014-2018 in New South Wales (NSW), Australia (n= 34 404), 2) 2008-2021 in Sweden (n = 97 986). ICS during pregnancy was measured as a dispensing in national medication registers. Exacerbation was defined as either an unplanned hospital visit for asthma, ≥ 5 short acting beta agonist or ≥1 oral corticosteroid dispensings. Child asthma was defined as a hospital diagnosis and/or ≥2 asthma medications. Hazard ratios were estimated using cox survival regression. Paternal exposures during the pregnancy and sibling analyses assessed unmeasured confounding. <bold>Results:</bold> Incidence rates for child asthma were 36 and 42 per 1000 person-years in NSW and Sweden respectively. In both populations the risk of child asthma was higher with an exacerbation in pregnancy (aHR 1.83 95%CI 1.62, 2.08 NSW, aHR 1.42 95%CI 1.36, 1.47 SWE) or ICS in pregnancy (aHR 1.39 95%CI 1.26, 1.54 NSW, aHR 1.29 95%CI 1.25, 1.33 SWE), adjusted for exacerbations. After adjusting for asthma severity the association with maternal exacerbations remained (aHR 1.27 95%CI 1.21, 1.34 SWE) and the association with ICS diminished (aHR 1.07 95%CI 1.03, 1.11 SWE). Paternal, sibling analyses confirmed these findings. <bold>Conclusion:</bold> Asthma exacerbations in pregnancy increase the risk of child asthma whereas ICS use in pregnancy is not associated with child asthma.