An ultrasound is a procedure that uses high frequency sound waves to scan the pelvic cavity and abdomen of a woman, and then creates a sonogram (a picture) of the placenta and the baby. The terms sonogram and ultrasound are technically very different. However, the two are used interchangeably.n ultrasound is a procedure that uses high frequency sound waves to scan the pelvic cavity and abdomen of a woman, and then creates a sonogram (a picture) of the placenta and the baby. The terms sonogram and ultrasound are technically very different. However, the two are used interchangeably.