Antepartum evaluations of the equine fetus.

Measurements were made by real-time ultrasonography in 14 healthy mares to assess fetal growth and estimate newborn foal weights. Intrauterine fluid volumes were estimated and the placenta was measured and observed for maturational changes. The onset and incidence of echogenic particles in the allantoic fluid were recorded. In the second approach, baseline fetal heart rate, physiological rate variations and number, amplitude and duration of recorded accelerations were measured. Estimates of birth weights were within +/- 3.49 kg. Allantoic fluid was evident in all sonographic planes within the uterine cavity. Average vertical axis was 1.9 +/- 0.9 cm. The mean thickness of the ventrally located gravid uterine horn and allantochorion was 1.26 +/- 0.33 cm. No placental maturational changes were noted. Echogenic particles were observed in the allantoic fluid of all mares recorded within 10 days of foaling. Baseline fetal heart rate was 76 +/- 8 beats/min. Spontaneous fetal activity resulted in accelerations in fetal heart rate from 25 to 40 beats/min in amplitude and of 23-36 sec in duration. About 10 accelerations were observed in a 10-min period. In 17 clinical case mares, abnormal records included decreased fetal activity; lack of fetal growth; haemorrhage and fibrin-like tags in the allantoic fluid; fetal tachycardia, bradycardia, arrhythmia, and cardiac deceleration. We suggest that ultrasonic fetal measurements provide useful information with regard to the fetal condition, but additional variables are required for more reliable assessments of fetal stress and distress.