A prenatal ultrasound test uses high-frequency sound waves, inaudible to the human ear, that are transmitted through the abdomen via a device called a transducer to look at the inside of the abdomen. With prenatal ultrasound, the echoes are recorded and transformed into video or photographic images of your baby. The ultrasound can be used during pregnancy to show images of the baby, amniotic sac, placenta, and ovaries. Major anatomical abnormalities or birth defects may be visible on an ultrasou