Pregnant horse ultrasound. Veterinarian scanning a pregnant mare's abdomen with a portable ultrasound system in order to monitor her foetus. The veterinarian is using a hand-held transducer (not seen) which emits high frequency sound waves that are reflected off internal structures in the horse's body. These sound reflections are detected and used to produce an image of the developing foetus on the monitor at lower left. Ultrasound can detect foetal disorders. It also helps to establish foetal size and development, and hence the expected date of delivery.