WOMEN with asthma, especially those with active symptoms during delivery, face higher risks of preterm birth, low birth weight, and cesarean delivery, according to a large population-based study of over 430,000 pregnancies in Canada.
The study analyzed 434,068 singleton live births in Alberta between 2009 and 2018, focusing on maternal asthma status and inflammatory phenotype to determine how each relates to adverse perinatal outcomes. Asthma was classified as ever (diagnosed more than one year before pregnancy), current (within one year or during pregnancy), or active (during delivery hospitalization). Researchers also examined immune phenotypes based on eosinophil and neutrophil blood counts.
Among the pregnant individuals studied, 8.6% had asthma. Of these, over half had ever asthma, 40% had current asthma, and 7% had active asthma during delivery. The adjusted risk of preterm birth was 15% higher in individuals with asthma compared to those without (adjusted relative risk [aRR]: 1.15; 95% CI: 1.11–1.20). Similarly, asthma was associated with an 11% increased risk of low birth weight (aRR: 1.11; 95% CI: 1.07–1.16) and a 10% increased likelihood of cesarean delivery (aRR: 1.10; 95% CI: 1.08–1.12).
The findings revealed a clear dose-response trend: risks were greatest in those with active asthma, followed by those with current and ever asthma. Notably, perinatal risk varied with immune phenotype. Pregnancies involving women with high eosinophil or neutrophil counts faced greater risk than those with lower counts, suggesting that inflammatory profiles may play a role in asthma-related complications.
These findings emphasize the importance of identifying and managing asthma in pregnant individuals, not only prior to conception but throughout pregnancy and delivery, to reduce the risk of adverse outcomes for both mother and infant.
Reference:
Moitra S et al. Maternal Asthma and Adverse Perinatal Outcomes: An Analysis of 434,068 Pregnancies in Canada. J Allergy Clin Immunol Pract. 2025;13(7):1836–1845.e6.
