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Pregnancy and mild asthma have minor effects on lung function

Published online: April 1, 2021

Lung function assessment offers a useful tool to monitor maternal health during pregnancy, especially given the unpredictability of asthma during this life stage. Spirometry is the most common technique used to assess lung function; however, the reference values used for comparison are based on non-pregnant populations. Hence, it is largely unclear whether lung function patterns change during pregnancy, and whether the patterns differ between women with and without asthma. Addressing this knowledge gap would provide evidence regarding the usefulness of spirometry during pregnancy to monitor maternal health.

In a recent issue of The Journal of Allergy and Clinical Immunology: In Practice, Jensen and colleagues provide original data on the effect of pregnancy, and the impact of asthma, on lung function patterns. In a combined cohort of 1,029 predominately white women in Eastern Australia, recruited between 12 to 22 weeks gestation and followed for the remainder of their pregnancy, the authors investigated whether lung function changes during pregnancy in women with current physician-diagnosed asthma (n=770, 75%) and women without asthma (n=259, 25%). The authors also examined whether asthma altered the pattern of lung function during pregnancy, controlling for maternal weight status, smoking status, and age. Lung function was measured using spirometry, collected at several time points, to provide a picture of lung function patterns across pregnancy.

As expected, baseline lung function was lower in women with asthma; however, the pattern of lung function over the remainder of pregnancy was only impacted marginally by either asthma or pregnancy itself. Pregnancy had minor, yet statistically significant, impacts on lung function, with lung function values generally decreasing as pregnancy progressed. Jensen and colleagues surmise that this is due to increasing restriction caused by the physiological changes that occur as pregnancy progresses. Interestingly, the authors found that the pattern of lung function during pregnancy was generally different in women with asthma, compared to women without asthma, with the minor negative effects of pregnancy opposed in the asthma group. Despite these findings, the pattern of lung function did not change meaningfully over the course of pregnancy in either women with or without asthma, with the largest change equating to a reduction in lung function of 5.6% over an entire pregnancy. These results provide evidence to support the use of spirometry to assess lung function during pregnancy, and its interpretation using existing reference values to monitor maternal health. However, the authors note that the women with asthma in this study were predominately well controlled and receiving active asthma management throughout pregnancy; thus, the results cannot necessarily be applied to women with poorly controlled or severe asthma, with future studies required in these groups.   

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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