Three-dimensional ultrasound assessment of fetal liver volume in normal pregnancy: a comparison of reproducibility with two-dimensional ultrasound and a search for a volume constant.

The purposes of this study are to compare the reproducibility of two-dimensional ultrasound (2DUS) and three-dimensional ultrasound (3DUS) in the assessment of fetal liver volume (LV), and to test whether the fetal LV assessed by the traditional method with 2DUS is equal to that with 3DUS in normal pregnancy. If significantly different, we then try to calculate a new constant of fetal LV for the traditional equation from the LV values obtained with 3DUS. In total, 30 normal singleton fetuses with gestational ages ranging from 20 to 30 weeks were included for the reproducibility test and 55 cases ranging from 20 to 31 weeks gestation were enrolled for finding a new volume constant of LV. The results showed that 3DUS is superior to 2DUS in the reproducibility test of fetal LV assessment. Moreover, the LV assessed with the traditional 2DUS method (identified as LV_42) was significantly smaller than that measured with 3DUS (P < 0.001). If the traditional 2DUS equation is to be used, the multiplying factor in the equation for the calculation of LV should be modified to 0.55 (SE = 0.017, N = 55). With the new volume constant, the new derived LV with 2DUS (identified as LV 55) was not different from that with 3DUS (identified as LV_3D). In conclusion, we recommend that 3DUS, instead of 2DUS, should be used for reaching an accurate assessment of fetal LV. Otherwise, applying our new volume constant may be of help in detecting abnormal fetal liver growth when only 2DUS is available.