Ultrasound examination offers a safe, reliable method of confirming pregnancy in the bitch and queen. Scanning is usually performed at 4 and 6 weeks after mating. Although examination at 20- 21 days can detect foetal heartbeats, by 28 days foetal membranes change position and foetal structures can be identified. Motion and mineralisation is noted between 31-33 days. Internal organs become recognisable at 33-36 days. Thoracic and abdominal cavities may be distinguished at 45 days. These developmental stages provide a guide to foetal age but are not a precise indicator of whelping/queening date.

Ultrasound is not a reliable method for counting foetuses. Radiography (x-rays) at 42 days is still a better method.

Ultrasound may also detect problems such as embryonic resorption, early foetal death, premature placental separation and pyometra.