Techniques and applications of transabdominal ultrasonography in the pregnant mare.

To establish the feasibility of utilizing high-frequency ultrasound to image equine fetal development transabdominally, in vitro and in vivo observations were made. Three fetuses retrieved from mares that died from various causes were scanned in vitro to establish fetal images from various orientations. A total of 50 mares ranging in age from 4 to 16 years and representing various breeds were scanned intermittently from 100 days of gestation to parturition. Fetal parts, amniotic fluid, placental membranes, and motion patterns could be reliably identified. Fetal heart rates decreased from 180 beats/min at 100 days' gestation to 60 to 80 beats/min from 2 weeks before parturition to term. Detection of fetal orientation, viability, and twin recognition represented practical applications of the technique.