The Doppler principle is used in pregnant animals from about 28 days. The Doppler principle, which is used by Medata, consists of an ultrasound beam directed against the sow orphan or the pulmonary artery that goes to the uterus. The vibrations that appear in the fetus or blood vessels are reflected back to the head of the head. The vibrations are transformed into the device, reproduced in headphones. In pregnant animals from approx. For 28-40 days, vibration (pulse beat) is heard from the pulse ulcer, while subsequent measurements hear heart sounds from the fetuses.