RESUMEN
AIM: To determine reference ranges for fetal lung volume by 3-dimensional ultrasonography using the VOCAL (Virtual Organ Computed-aided Analysis) method. METHODS: A longitudinal prospective study was conducted with 61 uncomplicated pregnancies between 24 and 32 weeks of gestation. A separate measurement of both lungs volume was conducted by VOCAL with 30 degrees rotation angle. For each gestational age, an average, standard deviation and maximal and minimal values were established in addition to the percentiles 5, 10, 25, 50, 75 and 90 for right and left lung volume. To evaluate the correlation between lung volume and gestational age, and estimated fetal weight, a polynomial regression with determination coefficient adjustment (R(2)) was used. The intra-observer reproducibility was evaluated by the intraclass correlation coefficient (ICC), whereas the inter-observer reproducibility was evaluated by Cronbach alpha statistic test. RESULTS: The average right lung volume varied from 12.5+/-0.7 cm(3) at the 24(th) week to 31.8 cm(3)+/-1.8 cm(3) at the 32(nd) week. The average left lung volume varied from 9.2+/-0.9 cm(3) at the 24(th) week to 22.0 cm(3)+/-1.6 cm(3) at the 32(nd) week. We observed a strong correlation between right lung volume and gestational age (R(2)=0.975) and estimated fetal weight (R(2)=0.905), as well as between the left lung volume with gestational age (R(2)=0.970) and estimated fetal weight (R(2)=0.908). We observed a good intra-observer reproducibility for the right lung volume (ICC=0.990) and for the left lung volume (ICC=0.986). Similarly, we observed good inter-observer reproducibility for right lung volume (0.975) and left lung volume (0.962). CONCLUSION: Reference range of fetal lung volume by 3D-ultrasonography using the VOCAL method was determined.