Longitudinal Analysis of Lung Function in Pregnant Women with and without Asthma

Spirometry is commonly used to assess and monitor lung function. It may also be a useful tool to monitor maternal health during pregnancy. However, large studies examining lung function across gestation are limited. Also, whether spirometry values follow the same pattern during pregnancy in women with and without asthma is unknown.

To investigate the effect of advancing gestation, and its interaction with asthma, on lung function in a large well-defined cohort of pregnant women.

Data were obtained from prospective cohorts involving women with (n = 770) and without (n = 259) asthma (2004-2017), recruited between 12 and 22 weeks' gestation. Lung function (forced vital capacity [FVC], FEV₁, FEV₁:FVC%) was assessed periodically during pregnancy using spirometry. Multilevel mixed-effect regression models were used to assess changes in lung function over gestation.

Asthma had a significant effect on baseline lung function (FEV₁%, -9%; FVC%, -3%; FEV₁:FVC%, -4%). FVC% decreased with advancing gestation (-0.07%/wk; 95% CI, -0.10 to -0.04]), as did FEV₁%, but only among those without asthma (women without asthma: -0.14%/wk, 95% CI, -0.22 to -0.06%; compared with women with asthma: 0.02%/wk, 95% CI, -0.01 to 0.06). FEV₁:FVC% remained relatively stable for women without asthma (0.03%/wk; 95% CI, -0.08 to 0.02), but increased for women with asthma (0.06%/wk; 95% CI, 0.04 to 0.16).

Data suggest that advancing gestation negatively affects FVC% and FEV₁%. This is consistent with extrapulmonary restriction from advancing pregnancy. Yet, the presence of asthma altered the trajectories of FEV₁% and FEV₁:FVC%. Optimal asthma management during pregnancy might have opposed the negative effects of gestation on lung function.