Examination of embryonic death in mares using colour Doppler and B-mode sonography

Embryonic death in mares was studied using colour Doppler sonography and B-mode sonography. The aim of this study was to characterize clinical symptoms for an impending embryonic death. In 6 Trotter mares, who have repeatedly been pregnant, the pregnancies were interrupted with a PGF2α analogue (Tiaprost) at Days 15, 25, 30 and 40. Three gestations were studied in each group (Day 30 with 4 gestations). After the PGF2α administration these mares were examined every 8 hours until the conceptuses were removed completely. Control groups, each made up of 3 pregnant mares, were examined daily. The size of the conceptus and the embryo/fetus, the thickness of the uterine wall, the embryonic heart rate and the Resistance Index (RI) of the A. uterina were recorded. The embryonic heart rate could be detected in some cases at Day 18 and in all cases at Day 20 with colour Doppler sonography. It increased from 97-111 beats/min at the first detection to about 167 beats/min at the end of the first month of pregnancy. Thereafter it reached a plateau for nearly a month and increased slightly to 176 beats/min at the end of the second month of pregnancy. The embryos of the treated mares (7 of 10) showed a bradycardia (64–130 beats/min) before death; 1 had a tachycardia (209 beats/min) and 2 had normal heart rates. Beginning on Day 15, the RI values of the ipsilateral (pregnant side) uterine artery were lower than those of the contralateral. In the course of early pregnancy the RI values of uterine arteries decreased further (P < 0.01). In the mares treated at Day 15 this phenomenon was not observed. In the mares treated at Day 25, 30 and 40, the difference between the ipsilateral and the contralateral uterine arteries, which was significant at the beginning, disappeared 24–48 hours before embryonic death. From PGF2α administration to embryonic death the treated mares had significantly higher RI values on the ipsilateral uterine artery than the untreated mares (P < 0.05). Sonographic characteristics of an impending embryonic death were as follows: the form of the conceptus became irregular and the thickness of the uterine wall was the same all around the embryonic vesicle. The endometrium became heterogen and estrous-like. A reduced volume of conceptual fluids, a strongly increased echogenity of the conceptual fluids and a disorganization of the conceptual membranes were the most important criteria after embryonic death.This study shows that colour Doppler sonography is a useful method to diagnose and predict embryonic mortality in mares. Compared to B-mode sonography, embryonic mortality can be detected earlier and more reliable with the colour Doppler technique.