Diagnosing asthma before vs during pregnancy might reduce preterm births

Published online: February 1, 2020

Uncontrolled asthma symptoms during pregnancy have been shown to increase the risk of poor infant outcomes such as low birth weight, congenital malformations, and preterm birth. While asthma that has been previously diagnosed can be managed with standard treatments during pregnancy, women who have latent asthma that has yet to be diagnosed could be more vulnerable to exacerbations from pregnancy-induced hormone fluctuations. It is unclear whether newly diagnosed asthma during pregnancy versus before pregnancy puts the fetus at higher risk of poor outcomes.

According to a recently published article in The Journal of Allergy and Clinical Immunology: In Practice, the timing of asthma diagnosis may have important clinical implications on birth outcomes. In a large population-based study, Longo and colleagues used administrative health data from over 122,000 Quebec women who were initially asthma-free and were followed from the 2 years prior to pregnancy onset until they successfully delivered between 1990 and 2010. The authors applied advanced statistical methods to mimic random assignment of an asthma diagnosis in each month of follow-up to evaluate whether women who were diagnosed during pregnancy had greater risks of preterm birth, small-for-gestational-age (SGA), and major congenital malformations, relative to those diagnosed in the 2 years prior to pregnancy.

The study found that in women with asthma versus without asthma, the risks of preterm birth were 34% and 93% higher in the second and third trimesters, respectively, while this was reduced to only 6-8% higher in those diagnosed in the first trimester or in the 2 years prior to pregnancy. Moreover, the findings also suggested that women diagnosed during the first trimester could be up to 18% more likely to deliver a baby with a major malformation than those without asthma; whereas there was no increased risk in women diagnosed prior to pregnancy. Although asthma was associated with an overall 6% modest increase in the risk of SGA, timing of diagnosis was not an important modifying factor of the asthma-SGA relationship.

Since receiving an asthma diagnosis in the second and third trimesters was associated with increased risks of preterm birth, which is a major cause of infant and childhood morbidity and mortality, this study suggests a potentially important role for asthma screening during preconception or very early during pregnancy in women who may have had a history of breathlessness or wheeze.

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.

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