Comparison of the two-dimensional and multiplanar methods and establishment of a new constant for the measurement of fetal lung volume

Abstract

Objectives. To compare the two-dimensional (2D) and multiplanar methods in the measurement of lung volume in normal fetuses, to obtain a new constant to be incorporated into the 2D equation, and to apply the new equation in fetuses with pulmonary hypoplasia (PH) confirmed postnatally.Methods. A cross-sectional study was performed on 51 pregnant women at between 20 and 35 weeks of gestation. The ellipsoid formula (x × y × z × 0.52) was used to calculate lung volume by the 2D method. A sequence of multiple planes with 2.0-mm intervals was used with the multiplanar method. In order to compare the techniques, the intra-class correlation coefficient (ICC) and the Student's t-test (p) were used. First-order linear regressions were used to establish a new constant, with three-dimensional (3D) lung volume as dependent variable and gestational age and 2D volume as independent variables. In order to validate it, the new equation was applied to 11 fetuses with confirmed lethal PH.Results. The mean volumes obtained by the 2D method were overestimated when compared to the multiplanar method (right lung: 23.87 vs. 18.26 mL, respectively, p < 0.001 and left lung: 16.18 vs. 14.33 mL, respectively, p = 0.008). Using a first-order polynomial regression, new constants were obtained for the right lung (0.152) and for the left lung (0.167). When compared to the traditional formula, the new equation presented higher sensitivity (18.1%) in predicting lethal PH.Conclusion. The recalculated 2D equation can be a promising alternative to 3D ultrasonography in the prediction of PH.