Comparison of two- and three-dimensional ultrasonography in lung volume measurement of normal fetuses.
OBJECTIVE
The purpose of this study was to compare the two- and three-dimensional methods for measuring fetal lung volume of normal fetuses.


METHODS
A cross-sectional study was performed with 51 normal pregnant women between 20 and 35 weeks. The ellipsoid formula (X*Y*Z*0.52) was used for volume calculation with the two-dimensional (2D) method. With the VOCAL (Virtual Organ Computer-aided Analysis) method, a rotation angle of 30 degrees was used. Intraclass correlation coefficient (ICC), paired Student's t-test and Bland-Altman plots were used to compare the techniques. To calculate the intraobserver variability we used the ICC and compared the means between the two measures using the paired Student's p-test.


RESULTS
VOCAL and 2D methods were highly correlated (ICC=0.919 and 0.873 for the right and left lungs, respectively), however, there was a disagreement. The fetal lung volume means calculated by the 2D method were always overestimated in relation to the means obtained by the VOCAL, for the right lung (24.02 mL x 19.15 mL; P<0.001), as well as for the left (16.03 mL x 13.77 mL; P=0.002). As for the intraobserver variability, a good reproducibility was observed for the volume measurement of the left lung by the 2D technique (mean=0.40 mL; P=0.57) and by the VOCAL (mean=-0.22 mL; P=0.63). The 2D method, however, presented low reproducibility for the right lung (mean=1.73 mL; P=0.31).


CONCLUSIONS
The two-dimensional method had low agreement and low reproducibility in relation to the three-dimensional method for measurement of fetal lung volume in normal fetuses.
Araujo Júnior
Edward
E
Department of Obstetrics, Sao Paulo's Federal University (Unifesp/EPM), Sao Paulo, SP, Brazil. araujojred@terra.com.br
Nardozza
Luciano Marcondes Machado
LM
Rodrigues  Pires
Claudio
C
Filho
Hélio Antonio Guimarães
HA
Moron
Antonio Fernandes
AF
D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008168:Lung / Q000000981:diagnostic imaging*; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D012016:Reference Values; D016216:Ultrasonography, Prenatal