Background: Forced expiratory volume in 6 s (FEV6) and FEV1/FEV6 ratio have traditionally been used as a surrogate for forced vital capacity (FVC) and FEV1/FVC in the assessment of spirometric lung function in nonpregnant subjects. However, the existence of this relationship during pregnancy is yet to be ascertained. Aim: The aim of this study was to determine if FEV6 and FEV1/FEV6 can effectively be used instead of FVC and FEV1/FVC in the interpretation of lung function test during pregnancy. Subjects and Methods: This study was a descriptive cross‑sectional study carried out among 200 pregnant women who were recruited by using systematic random sampling during the period between April and October 2011. One hundred matched nonpregnant women served as control. A standard spirometer was used to determine the FVC, FEV6, FEV1/FVC, and FEV1/FEV6. Data analysis was done using SPSS version 11.0 (Chicago, IL, USA). Values were recorded as mean (standard deviation), and also median and interquartile ranges. The one‑way analysis of variance, Mann–Whitey U and the Kruskal–Wallis were used to test for significance where applicable. P <0.05 were considered to be significant. Results: All the values were within normal range, but the FVC and FEV6 decreased significantly while the FEV1/FVC and FEV1/FEV6 increased as pregnancy progressed. However, for first and last trimester, FVC differed significantly from FEV6. The values of the FVC were comparable to the values of FEV6. The FEV1/FVC and FEV1/FEV6 ratio were similar and well above the 0.7 cutoff for obstructive lung diseases. Conclusion: FEV6 requires a short exhalation time and can effectively be used in place of FVC in evaluation of lung function test during pregnancy. The FEV1/FEV6 may be applied as a proxy for FEV1/FVC in pregnant and nonpregnant women.
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