Real-time ultrasonic biparietal diameter of second trimester Suffolk and Finn sheep fetuses and prediction of gestational age.

Six Suffolk fetuses of known gestational age were examined every other day from Day 43 to Day 96 of gestation using transabdominal real-time ultrasound. Biparietal diameter (BPD) was measured on symmetrical fetal head images. The relationship between days gestational age (GA) and mean BPD in millimeters is described by the equation: [GA = 22.5 + 1.81 BPD]. Repeated ultrasound examination of 9 Finn ewes between 35 and 95 d of gestation revealed the relationship: [GA = 21.4 + 1.85 BPD]. Biparietal diameters were determined for 56 Suffolk X Hampshire fetuses which ranged from 41 to 77 d of gestation. The predicted fetal age using the Suffolk equation was within 1 d of the recorded age for 22 56 , +/-2 d for 34 56 , and +/-3 d for 44 56 fetuses.