Real-time ultrasonic biparietal diameter measurement for the prediction of gestational age in llamas.

Llama (Lama glama ) fetuses (n = 25) of known gestational age (Day 66 to Day 235) were examined transabdominally using real-time ultrasound with a 5 MHz linear-array scanhead. Maximum head width, or biparietal diameter (BPD), was measured in symmetrical images using electronic linear distance calipers. The fetus was easily located and the BPD measured as early as Day 66 of gestation. During the last trimester, measurement became increasingly difficult due to the posture of the fetus and the limited penetration of the 5 MHz frequency. The relationship between days of gestational age (GA) and mean BPD in millimeters is described by the equation: [GA = 18.8 + 3.79 BPD]. Assignment of gestational age allows estimation of parturition date in this frequently pasture-bred and newly polular domestic ruminant.