Twin pregnancies in horses can be incredibly risky—even deadly—for mare and fetuses alike, so it’s important to detect them early and take appropriate steps to achieve a positive outcome. However, it can be challenging to diagnose twins using traditional ultrasound, said PhD candidate and predoctoral fellow Lisse Vera, of the Ghent University Faculty of Veterinary Medicine, in Merelbeke, Belgium. Fortunately, she and colleagues, have confirmed that clinicians can detect two fetal heart beats on electrocardiograms (ECG) if they place electrodes carefully.

Detecting Twins

Twin pregnancies occur when mares double ovulate, meaning they release two eggs in the same cycle, Vera said. That happens in about 25% of heat cycles in Thoroughbreds and Warmbloods, although many of those don’t result in twin pregnancies. When they do, veterinarians often identify them through ultrasound checks in the second week of pregnancy and eliminate a twin by pinching it.

Most twin pregnancies, if not reduced to a single pregnancy, result in abortion, stillbirth, or weak and nonviable foals, Vera said.

While transrectal ultrasound can identify twin pregnancies very early during the embryonic stage, this method is less effective at detecting two fetuses once they’ve grown too large. And transabdominal ultrasound (using the ultrasound probe against the abdominal wall) might allow scientists to get a glimpse of a foal—if it’s not hidden behind the mare’s intestines. But to diagnose a twin pregnancy, it’s important to see both foals at the same time, Vera said. Otherwise, only seeing one foal at a time could be confused with seeing the same foal