Pregnancy does not affect progression of mild experimental asthma in sheep

Asthma is the most common respiratory condition during pregnancy and increases the risks of adverse pregnancy and perinatal outcomes. Asthma symptoms change in ∼60% of pregnancies, but whether this is due to pregnancy itself is unclear. We tested the hypothesis that physiological changes during pregnancy worsen asthma severity in an ovine experimental model of allergic asthma. Three-year-old Merino ewes were randomly allocated to either control or allergic asthma groups. Asthma was induced through sensitisation and repeated airway challenge with house dust mite allergen. We compared airway function, circulating cytokine profile and airway immune response to allergen challenge throughout the study and airway structure between groups, in non-pregnant (control n = 8, asthma n = 9), singleton-pregnant (control n = 5, asthma n = 8) and twin-pregnant ewes (control n = 6, asthma n = 9). Within non-pregnant animals, transpulmonary pressure at Day 132 of the study was 37% higher in asthmatic than control ewes (P = 0.031), but not different between treatments in singleton-pregnant (P = 0.594) or twin-pregnant (P = 0.074) ewes. Between premating and Day 132, dynamic compliance decreased more in asthmatic than control ewes (P = 0.040), and this change did not differ between litter sizes (P = 0.096). Neither asthma nor pregnancy affected eosinophils in bronchoalveolar lavage or lung tissue. There was no evidence of lung airway remodelling in the cohort. The results of this study suggest that pregnancy does not increase asthma symptoms or severity of mild asthma. KEY POINTS: Asthma severity changes in ∼60% of pregnancies, but whether this is due to pregnancy itself is unclear. Using a sheep model of allergic asthma, we tested the hypothesis that physiological changes during pregnancy worsen asthma severity. Dynamic compliance decreased to a greater extent in asthmatic than control ewes over the course of the study, indicating the development of a mild asthma phenotype, and this decrease was similar in non-pregnant, singleton-pregnant and twin-pregnant ewes. Eosinophil proportions in bronchoalveolar lavage and lung tissue were not affected by either asthma or pregnancy, nor was there evidence of lung airway remodelling in this cohort. Our findings suggest that pregnancy does not increase asthma symptoms or severity of mild asthma.