FETAL HEART-VOLUME ASSESSMENT BY 3-DIMENSIONAL ULTRASOUND

Heart volume may provide important information on the status of fetal hemodynamics. However, traditionally fetal heart volume has been asses sed with the erroneous assumption that the fetal heart is spherical or elliptical. With the advent of three-dimensional ultrasound, accurate assessment of organ volume has become feasible. The objectives of thi s study were to compare the reproducibility of two-dimensional ultraso und and three-dimensional ultrasound in the assessment of heart volume , and to test whether heart volume assessed by the traditional method of two-dimensional ultrasound equates to that assessed by three-dimens ional ultrasound. If it proved to be significantly different, we aimed to find a new constant which, if incorporated into the traditional fo rmula used to determine heart volume, would enable us to achieve more accurate volumes with two-dimensional ultrasound. In total, 50 normal singleton fetuses ranging from 20 to 30 weeks' gestation were included in the study. Both the traditional two-dimensional and the new three- dimensional volume measurements were compared The results showed that three-dimensional ultrasound has a better reproducibility than two-dim ensional ultrasound in heart volume assessment and that heart volume a ssessed by the traditional formula of two-dimensional ultrasound is si gnificantly larger than that measured by three-dimensional ultrasound (p < 0.001). We therefore propose that, if the traditional two-dimensi onal equation is to be used the constant for heart volume could be mod ified to 0.4563 (SE = 0.0153, n = 50) to achieve more accurate results . With this new constant, the heart volume derived by two-dimensional ultrasound was not found to differ from that measured by three-dimensi onal ultrasound. From our series, we conclude that: three-dimensional ultrasound is theoretically the best method for the assessment of hear t volume. However, because of the limitations of three-dimensional ult rasound (i.e. it is not routinely available, if is more expensive and more time-consuming) two-dimensional ultrasound in practical terms sho uld be she method of choice. Although we were able to improve the accu racy of the heart volume measurements using a new constant in the trad itional two-dimensional formula, the new constant will not improve var iability, which can only be reduced by three-dimensional ultrasound.