How Does a Prenatal Heart Monitor Work?

A prenatal heart monitor works using what is known as the "doppler effect." The doppler effect refers to the changing of the pitch of a sound when the source of that sound is moving either away or towards the person listening to the sound. For example, think of how the sound of a constant train or car horn will change as it comes near to you and then moves away again.

The doppler effect is used in many types of scientific theories and practices. For example, astronomers use the doppler effect to measure whether stars and galaxies are moving towards or away from us, and some forms of radar also use the doppler effect to catch people speeding in cars. With a baby heart monitor, the doppler effect is put into practice to allow you to hear your unborn baby's heart clearly and strongly.

Most prenatal heart monitors require that you use some ultrasound gel with the monitor, so be sure to purchase the gel at the same time that you get your monitor.

To use a baby heart monitor, place a small amount of gel on your abdomen. Then put the sensor head on top of the gel on your abdomen and slide it around until you find the baby's heart beat. It may take a few tries before you find the baby's heart, but it becomes much easier after a few times. Remember, however, that most baby heart monitors are not suited to pick up a baby's heartbeat until 10 to 12 weeks or later. The video to the right shows an affordable AngelSounds baby heart monitor in use by a pregnant woman on herself.