ABSTRACT Objective Complications in pregnancy are suggested to be the result of intrauterine conditions in the first trimester of pregnancy. Three-dimensional ultrasound volume measurements might give more information, compared with two-dimensional measurements. Commonly available methods for volume measurements are not suited for daily practice. This is a report of preliminary results of a promising, more practical semi-automated method for volume calculations with three-dimensional ultrasound. Method Volume datasets of 16 objects (10.2–41.5¿cm3) were obtained. Euclidean shortening flow and Perona and Malik were used as image enhancement techniques. The image gradient was calculated. The points of interest were detected by the iso-intensity and the edge-detection technique. Volume measurements with Volume Computer-aided AnaLysis (VOCAL) are used as a reference. A volume dataset of a first trimester fetus was acquired to test this method in vivo. Results The mathematical calculations with iso-intensity (Perona and Malik: average¿=¿-1.57¿cm3, SD¿=¿4.05; and Euclidean shortening flow: average¿=¿-1.38¿cm3, SD¿=¿2.47) showed results comparable with the VOCAL method (average¿=¿+1.28¿cm3, SD¿=¿2.07). We also succeeded in detecting all voxels in the whole contour of a 12-week fetus. Conclusion Mathematical volume calculations are possible with the semi-automated method. We were able to apply this new method on a first trimester fetus. This new method is promising for future use in the daily practice. © 2012 John Wiley & Sons, Ltd.