Normal Fetal Lung Volume Determined by Three- Dimensional Ultrasonography using Virtual Organ Computer-Aided Analysis at 22-37 Weeks’ Gestation

Objective: To establish a reference of normal fetal lung volume using three-dimentional ultrasonography in the second half of pregnancy. Methods: A prospective longitudinal study was conducted in 53 Thai healthy singleton pregnant women at 22-37 weeks of gestation. By using 3-D ultrasonography with Virtual Organ Computer-Aided Analysis (VOCAL), the whole fetal thorax was obtained as volume data and then calculated in each participant for 3-6 successions. Our method showed excellent intraclass correlation coefficients (ICC = 0.990-0.991) among three operators and validity ranged within 3% of the actual volume. Multivariate analysis was used to identify the relationship between lung volume and gestational age. This longitudinal data set was then analysed by mixed model regression analysis. Results: A total of 260 fetal lung volumes were obtained. Average maternal age, gestational age and birth weight were 26.9 ± 4.7 years, 38.9 ± 1.3 weeks and 3,007.5 ± 349.3 grams. With mixed model of regression analysis, the relationship between lung volume and GA was demonstrated as follows: left lung volume (ml.) = (-12.19) + (0.22*GA) + (0.03*GA2), right lung volume (ml.) = (-24.91) + (1.19*GA) + (0.02*GA2), total lung volume (ml.) = (-37.32) + (1.43*GA) + (0.05*GA2). Conclusion: This is the normal fetal lung volume in the Thai population using the rotational technique (VOCAL). It could be considered as a reference for prenatal diagnosis of pulmonary hypoplasia.