This quick video clip illustrates the difference between the appearance of gestation sacs and intestines on a canine or feline ultrasound scan. Note the 'hamburger' shape of the intestines, which would appear tubular with rotation of the probe by 90 degrees. The pregnancy sacs, on the other hand, are circular at this early stage (30 days) and would maintain their distinct borders even with rotation of the transducer.

The liver can also be seen at the top of the screen.

 

 

Once you find the gestation sacs, it is important to check for viability (look for a heartbeat). Even at this very early stage, the puppy's beating heart is visible: