Fetal lung volume: comparison by 2D- and 3D-sonography in normal fetuses

Abstract

To compare two-dimensional ultrasonography (2D US) and three-dimensional ultrasonography (3D US) in the assessment of normal fetal lung volume. A cross-sectional study was performed involving 50 normal pregnancies at 24-32 weeks' gestation. The following equations were used for lung volume calculation by 2D US: Eq(2D1) = 4.24 + {1.53 x [(area of base of both lungs) x 1/3 (height of right lung)]} and Eq(2D2) = [anteroposterior diameter (X) x transverse diameter (Y) x cranial-caudal diameter (Z) of the right lung x 0.152 + (X') x (Y') x (Z') of the left lung x 0.167]. For 3D US, the virtual organ computer-aided analysis (VOCAL) method was used with a 30 degrees rotation angle and the total lung volume (V3D) was obtained by summing the volumes of each lung. Regression models (R (2)) were devised to assess lung volume evolution over the course of the pregnancy. Pearson's correlation coefficient (r) was used to assess correlation among the techniques, while Friedman's test was used for means comparisons. Strong correlation was observed among the three techniques [V3D vs. Eq(2D2) r = 0.856; V3D vs. Eq(2D1) r = 0.838 and Eq(2D2) vs. Eq(2D1) r = 0.964; all with P < 0.001]. Mean lung volumes were 37.05 +/- 9.67, 29.79 +/- 8.79 and 12.67 +/- 4.12 ml for V3D, Eq(2D1) and Eq(2D2), respectively (P < 0.001). Strong correlation and significant difference was observed among the three techniques of fetal lung volume assessment in normal fetuses.