What is a Prenatal Doppler?

J.M. Densing

A prenatal doppler is a device used to listen to the heart of the developing fetus inside the uterus of a pregnant woman. It uses an ultrasound transducer and the doppler effect to produce an audible representation of the fetal heartbeat. Some models can also calculate the heart rate and record the sound of the heartbeat. The prenatal doppler is easy to use and poses no risk to the developing baby. While it is commonly used in the doctor's office for prenatal care, some expectant mothers rent or buy their own for home use.

A prenatal doppler is often used in a doctor's office to listen to the fetus' heartbeat.
A prenatal doppler is often used in a doctor's office to listen to the fetus' heartbeat.

A typical prenatal doppler unit, also known as a fetal doppler or fetal heart rate monitor, consists of two main parts. One part is an ultrasound transducer which is used as a probe to find the heartbeat. It often has a cylindrical shape with a widened flat end, and it emits and receives sound waves. The second part is a receiver and control unit, which is usually a box with several buttons that control the unit, a speaker; it occasionally has a display to show the heart rate.

Using transducer gel for an ultrasound allows for ultrasound waves to penetrate through the skin and muscle.
Using transducer gel for an ultrasound allows for ultrasound waves to penetrate through the skin and muscle.

The prenatal doppler works in a different manner than an acoustic fetal stethoscope. The ultrasound transducer is used as a probe to find the heartbeat with sound waves which are reflected back. This reflection of the sound waves to provide information about a sound or object is known as the doppler effect. The monitor then uses this information to recreate the sound so that it can be heard over a speaker in the unit.

In addition to creating an audible representation of the heartbeat for all to hear, prenatal doppler units can perform other functions. Some units are able to calculate the heart rate and display it on a screen as beats per minute. If a unit doesn't perform this function, the heart rate is easy to calculate by counting the beats for ten seconds and then multiplying by six to get the heart rate. Some units are also able to record the sound of the heartbeat, which then can be downloaded to the parent's computer so that it can be shared with friends and family.

Used at the doctor's office or at home, a prenatal doppler is simple to operate. First, ultrasound gel is applied to the mother's belly to aid in the transmission of the sound waves, and then the probe is moved slowly around in a circular motion until the heartbeat is located. The probe is then held in place to listen. These devices are considered to be a safe and routine part of prenatal care, and many mothers look forward to hearing the sounds of their baby's heart at each visit. For mothers who want to listen at home to reassure themselves of their baby's health, units are available to purchase or rent

A prenatal doppler uses an ultrasound transducer and the doppler effect to produce an audible representation of the fetal heartbeat.
A prenatal doppler uses an ultrasound transducer and the doppler effect to produce an audible representation of the fetal heartbeat.

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