Contrast-Enhanced Ultrasonography of the Uterus During Normal Equine Pregnancy: Preliminary Report in Two Mares

There are no reports on use of contrast-enhanced ultrasonography (CEUS) in equine obstetrics. The aim of this study was to evaluate feasibility and safety of CEUS as a technique for monitoring and quantifying perfusion of the uterus throughout normal pregnancy in mares. Two pregnant Standardbred healthy mares underwent real-time two-dimensional ultrasonography, Doppler ultrasound, and CEUS of the uteroplacental unit on day 40, at 90-100 days, then every 30 days, and every 10 days during the last month of pregnancy. Foeto-placental well-being and in particular fetal heart rate as an index of fetal stress were monitored, and main uterine arteries diameter and Doppler parameter resistance index (RI) were measured. Contrast-enhanced ultrasonography quantitative perfusion variables, peak intensity, arrival time, time to peak from injection, and time to peak from initial rise were measured. No contrast medium was observed in the fetus, umbilical vein, and allantochorionic layer of the uteroplacental unit. Neonatal foals were clinically normal. Placenta was normal at postpartum gross examination in both mares. A progressive bilateral increase in diameter of the uterine arteries was noticed for both mares. The Doppler RI reduced early during the first half of the pregnancy and then remained relatively unchanged until delivery. Contrast enhancement was satisfactory in all CEUS. Peak intensity showed overall fivefold and 10-fold increase throughout pregnancy in mare no. 1 and no. 2, respectively. No discrete trend of change was noticed for other CEUS variables. Contrast-enhanced ultrasonography is feasible and seems safe to study microperfusion of the uterus during normal pregnancy in mares.