What is a fetal doppler?

Generally, fetal doppler is a popular and non-invasive diagnostic device to monitor the fetus, including detecting and measuring the heart rate. Its operation is based on Doppler Effect, which emits and receive continuing ultra-sonic sound waves and then emits the shift or change in their pitch rate.


Every fetal doppler is made with a probe or transducer of changing MGHZ, including piezo-electric crystals that transmit short sound beats to the specific position of the body. Each time one of those sound waves are transmitted, the probe or transducer would stop for a short time and wait for the returning reflection. Then, the fetal doppler will measure the direction and depth of every returning reflection wave and convert the signal to the heart rate of fetus that you hear.

When could you start to use a fetal doppler?

In several people, the heart rate of a fetus could be determined after 8 to 12 weeks of pregnancy. In general, you could hear the heartbeat of a fetus clearly after 14 weeks.

To find the heart rate from 8 to 12 weeks, one of the decisive factors is the quality of the fetal Doppler. A probe with 3 MGHZ tends to get the fetal heartbeat later than a device with 2 MGHZ since it is made with a less defined beam that would penetrate shallower (1 to 2 centimeters compared to 3 to 5 centimeters).

Another important thing to bear in mind is that nobody is the same, so it is not a reason to worry if you could not find the heart rate of your baby. As mentioned above, all of women would be able to hear their fetal heart rate after 14 weeks of pregnancy.

How often should you use a fetal doppler?

Prudence is always an important thing. When it comes to using a fetal Doppler, it is often recommended to use it infrequently, in short interval and after your first trimester.In general, you should not use a fetal Doppler for more than 10 minutes in each examination. Have a break if you could not still determine the heart rate during this time.

How do you know that you are hearing the baby's heart rate, not yours?

The most effective and also easiest method to determine the heartbeat of a baby would be using the beats per minute (BPM) or heart rate. In general, the normal heart rate of a baby would be in the range from 120 to 180 bpm. Conversely, this range in a pregnant woman would be from 60 to 100 bpm.

In early stage, the heart rate of a fetus is normally different in a sensible range. As the pregnancy develops, this range would get more static. In addition, the heart rate of a baby would also depend on the level of activity.

Why do you need to use ultrasound gel?

It is compulsory to use ultrasound when you are doing an examination by the fetal doppler. In general, ultrasound gel is particularly made to work as the coupling part and decrease the static which is usually generated when applying the fetal doppler.

To receive optimal sound and use from the fetal Doppler, you should apply a lot of ultrasound gel. Never apply lotion or colored gel. If the fetal Doppler is used with any substances with oil, it would damage the probe as well as lead to excess static. In fact, you would cost 300 USD to replace a probe simply because it is one of the most important elements of a fetal Doppler.

How to use a fetal doppler:

1. Expose the belly down to the pubis. In fact, the womb is still very low and a pelvic part.

2. Apply on the lower belly lots of ultrasound gel to help a fetal doppler work better.

3. Place the doppler wand on the belly before you turn on the device. This would help to cut down noisy static effectively when you turn on the machine. To begin, put the wand no more than one inch from the hairline.

4. Use the first mode to determine the HB. It would indicate real time bpm. After finding the heartbeat of the baby, you could turn to the second mode to get more precise heart rate.

5. Turn up the volume. You might hear the heartbeat briefly before it appears on the screen. All that you need to guide is the sound.

6. While you are leaving the wand’s head on the belly, move it around on a circle.

7. If you would not find it, then move over the head to the right or left a little bit and move it around again.

8. Always remember to keep patience. Measure the time and spend no less than 5 minutes every time you to the task.

​Extra tricks and tips

  • Remember to keep the paper towel in reach.
  • Most of the baby's are not precisely in the middle. In fact, some people believe that a boy would be on the right and a girl would be on the left.
  • You should try this task with an empty or full stomach and bladder.
  • Try the first time after sleeping or in the morning when you have least bloat. If this does not work, then you should try it at the end of the day. As mentioned, everybody is not the same.
  • A mother with plus size could still determine the heartbeat of the baby in early stage. What you need to do to press harder. Maybe it might take more time and practice for this task, but you could definitely do it.
  • If you get the heart rate in the range from 60 to 100 bpm, then that is probably not your baby but you.
  • The sound of you baby's heart rate is similar to the galloping horse, particularly in early stage. In other words, it is really fast.

Nancy D. Richardson

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