How Ultrasound Works

By: Craig Freudenrich, Ph.D.  | 

Major Uses of Ultrasound

Ultrasou­nd has been used in a variety of clinical settings, including obstetrics and gynecology, cardiology and cancer detection. The main advantage of ultrasound is that certain structures can be observed without using radiation. Ultrasound can also be done much faster than X-rays or other radiographic techniques. Here is a short list of some uses for ultrasound:

Obstetrics and Gynecology

  • Measuring the size of the fetus to determine the due date.
  • Determining the position of the fetus to see if it is in the normal head-down position or breech.
  • Checking the position of the placenta to see if it is improperly developing over the opening to the uterus (cervix).
  • Seeing the number of fetuses in the uterus.
  • Checking the sex of the baby (if the genital area can be clearly seen).
  • Checking the fetus's growth rate by making many measurements over time.
  • Detecting ectopic pregnancy, the life-threatening situation in which the baby is implanted in the fallopian tubes instead of in the uterus.
  • Determining whether there is an appropriate amount of amniotic fluid cushioning the baby.
  • Monitoring the baby during specialized procedures — ultrasound has been helpful in seeing and avoiding the baby during amniocentesis (sampling of the amniotic fluid with a needle for genetic testing). Years ago, doctors use to perform this procedure blindly; however, with the accompanying use of ultrasound, the risks of this procedure have dropped dramatically.
  • Seeing tumors of the ovary and breast.


  • Seeing the inside of the heart to identify abnormal structures or functions.
  • Measuring blood flow through the heart and major blood vessels.


  • Measuring blood flow through the kidney.
  • Seeing kidney stones.
  • detecting prostate cancer early.

In addition to these areas, there is a growing use of ultrasound as a rapid imaging tool for diagnosis in emergency rooms.


There have been many concerns about the safety of ultrasound. Because ultrasound is energy, the question becomes "What is this energy doing to my tissues or my baby?" There have been some reports of low birthweight babies being born to mothers who had frequent ultrasound examinations during pregnancy. The two major possibilities with ultrasound are as follows:

  • Development of heat— tissues or water absorbs the ultrasound energy which increases their temperature locally.
  • formation of bubbles (cavitation)— when dissolved gases come out of solution due to local heat caused by ultrasound.

However, there have been no substantiated ill-effects of ultrasound documented in studies in either humans or animals. This being said, ultrasound should still be used only when necessary (i.e. better to be cautious).