Equine fetal gender determination in mid- and advanced gestation by transabdominal approach - comparative study using 2D B-Mode ultrasound, Doppler sonography, 3D B-Mode and following tomographic ultrasound imaging

Gender determination of the equine fetus is of big interest for the owner of a mare, particularly when planning the breeding purposes or due to economic reasons. This study aims to evaluate the feasibility of transabdominal 3D tomographic ultrasound imaging (TUI) as an additional diagnostic tool for gender determination. Special reference should be given to the hands-on experience of the examiner in the non-invasive transabdominal approach. Pregnancy checks were performed on 669 mares on various Thoroughbred stud farms in the mid-west of Germany in 2015 and 2016. Fetal sex was determined by 2D B-Mode ultrasound, 2D Doppler sonography and 3D imaging. Fetal gender was determined in a serial examination; time for each mare was limited to a maximum of 3 minutes. Predicted gender in 2015 and 2016 was compared to the gender at birth to determine accuracy of the methods. Transabdominal sonography was performed on 386 pregnant mares in 2015 and 283 mares in 2016. The gender of the fetus could be determined in 297 (~77 %, year 2015) and 184 cases (~65 %, year 2016) respectively, within the three-minute examination time frame. 3D imaging was realized in 118 (~40 %, year 2015) and 94 cases (~51 % year 2016) respectively. Combined transabdominal examination with B-Mode, Doppler and 3D TUI analysis led to high accuracies of correct gender diagnosis (~94 % (2015) and ~96 % (2016)). 3D TUI imaging allowed a gender diagnosis in 18 cases where B-Mode and Doppler sonography showed doubtful results (2015). 3D TUI of the fetal gonads was shown to be useful to increase the accuracy of gender determination in mares during mid- and advanced-gestatio