Spirometric Changes during Pregnancy in Cystic Fibrosis Patients

Rationale: Survival and longevity in patients with cystic fibrosis (CF) have improved with new treatments, so that pregnancy can be safely undertaken despite physiologic limitations. Dyspnea still develops in the latter stages of pregnancy. To explain this symptom, we evaluated the effect of pregnancy on lung function before and after delivery. Methods: Records of 23 pregnant patients with CF were retrospectively reviewed for data analysis. Spirometry was recorded prior to pregnancy, at first and third trimesters, and every three months following delivery up to one year. Comparisons between time points were adjusted for age and pre-gestational BMI by analysis of variance (ANOVA). Results: Complete clinical and spirometric data were available for eleven of these patients (13 pregnancies total), obtained between 2009 and 2017. FEV1 and FVC declined significantly from baseline to third trimester (by 8.1%, p < 0.043 and 9.3%, p < 0.013, respectively). No statistically significant differences amongst spirometric values were observed, however, when adjusted for BMI and age over the entire time course. FEV1 and FVC recovered to baseline six months and one year following delivery, respectively. Conclusions: The changes in FEV1 and FVC occur as a result of increases in intravascular blood volume and lung water during the third trimester. At the same time, FEV1/FVC increases as there is reversal of bronchiolar constriction with elimination of extracellular fluid and lung water. Furthermore, restoration of end-expiratory lung volume post-partum counteracts reversal of air trapping with resolution of peribronchiolar edema, with FVC remaining unchanged. These changes would explain decrease in dyspnea following delivery in CF patients.