Ultrasound is a technique that uses ultrasonic pressure waves at a very high frequency to view internal organs. Ultrasound is used to examine organs or structures that won't show up on X-rays. Because it doesn't produce harmful radiation like X-rays do, it's useful for monitoring the developing fetus during pregnancy. To begin this painless procedure, you lie face up or face down, depending on the organ that's to be studied. A lubricant is smoothed over the appropriate area of the body, and a transducer, which looks like a microphone, is pressed back and forth over the lubricated area. Images then appear on a monitor,and photographs are taken at specific intervals by the attending technician. Ultrasound is also used during amniocentesis (am-nee-oh-sin-TEE-suss) to determine the position of the fetus, so a needle can be safely guided into the amniotic (am-nee-OT-ick) sac to obtain a fluid sample. For more information on ultrasound procedures, consult a health care professional.