An ultrasound scan is a medical exam that uses high-frequency sound waves to capture live images from the inside of your body. The sound waves are at too high of a pitch for the human ear to hear.

Also known as sonography, an ultrasound is a noninvasive, painless procedure that produces images of organs, soft tissues, blood vessels, and blood flow, from inside the body. These images are used for medical analysis. Unlike other imaging techniques, ultrasound uses no radiation. For this reason, it’s the preferred method for viewing a developing fetus during pregnancy.

To prepare for the exam, you will most likely be lying down on a table with a section of your body exposed. Depending on the area being examined, you may need to change positions during the exam to allow the technician to have better access.

An ultrasound technician, called a sonographer, will apply a special lubricating jelly to your skin. This prevents friction and helps transmit the sound waves so the ultrasound transducer can rub across the skin area. The transducer has a similar appearance to a microphone and sends high-frequency sound waves through the body. The waves echo as they hit a dense object, such as an organ or bone. Those echoes are then reflected back into a computer image. The images can provide valuable information for diagnosing and directing treatment for a variety of diseases and conditions.

Sometimes, ultrasounds are done inside your body. In this case, the transducer is gently inserted into a natural opening in your body. To evaluate pregnancies under 12 weeks, the medical standard is a transvaginal ultrasound, which means the transducer is gently inserted into the vagina in order to view the uterus, fetal development, and ovaries.