How Fetal Dopplers Work

Fetal Doppler technology is based on the Doppleshift principle. This theory was first discovered by Christian Doppler an Austrian physicist in 1842. Doppler discovered that sound waves from a moving source would be compressed or expanded, or that the frequency would change.
Doppler work on the principle of listening to reflections of small, high frequency sound waves (ultrasound). These ultrasound waves are generated by microscopic vibrations of piezoelectric crystals. When the waves are reflected from moving objects, such as a foetal heart the frequency changes slightly. It is this change that is analysed by the electronics of the Doppler and converted into a sound that you can hear or a digital display of the heart rate.

Is fetal doppler use safe for my baby?

Yes, Meditech Doppler are manufactured by industry leaders and meet or exceed the standards s. They are approved for personal use at home and do not require a prescription. The waves emitted by a fetal doppler are far lower than those put out by an ultrasound (sonogram) machine and use probes at a much lower frequency. As always with any questions regarding your pregnancy, if you have any concerns about the safety of Fetal Dopplers we suggest you consult with your healthcare provider.   

What is the difference between a Fetal Doppler and an Ultrasound Machine?

There appears to be some confusion surrounding the perceived differences between the ultrasound machines (sonogram machines) used to obtain an image and fetal heartbeat monitors which allow you to listen to your baby's heartbeat.

 Although both technologies use sound waves to obtain information, the waves from an ultrasound machine are much, much higher (over 40 times higher) than that of a fetal heartbeat monitor. Also, the frequency and variation of probe use (between 2,5-10 MHz probes) and output levels (up to 740 watts) require that only a trained ultrasound technician should perform an ultrasound whereas a fetal heartbeat monitor only has few probe (2,3,4,8 MHz) and one output level (less than 20 watts) so it can be easily and safely used by anyone.

Also, a fetal doppler  is not the same thing as a blood flow doppler (used to check for abnormalities in the umbilical cord). Ultrasound machines used to obtain pictures along with fetal doppler umbilical cord testing are medical procedures that should only be performed by a licensed technician. Fetal heartbeat monitors have been used for well over 50 years and are approved for use at home by pregnant women

If you have any further questions or concerns regarding the rental of a fetal doppler for home use please call or email us or speak with your healthcare provider.

How early can your dopplers detect the heartbeat?

Our dopplers are same top of the line, medical grade dopplers that your doctor uses and are able to detect a fetal heart rate as early as 8-10 weeks. However, due to factors such as, the position of the fetus, size and shape of mother's uterus, size of the mother's body some people may not be able to hear the heartbeat until closer to 10-12 weeks (very tall and/or overweight people may have more difficulties hearing the heartbeat before 10 or 12 weeks). It really depends on so many factors as to how early you will hear the heartbeat but on average, most people find the heartbeat pretty easily and say that our dopplers are very easy to use. 

Of those surveyed:

15% were able the hear the heartbeat at 7 weeks

75% were able to hear the heartbeat at 8 weeks

85% were able to hear the heartbeat at 9 weeks

95% were able the hear the heartbeat at 10 weeks

99% were able the hear the heartbeat at 11-12 weeks

Why use a 2 MHz probe?

 2Mhz probe is better for picking up an early heartbeat in overweight people. After 12 weeks though there is usually no difference in 2 or more MHz probes. Once the baby moves up out of the pelvic region (after about 12 weeks) the heartbeat is pretty easy to find with either probe.

If you are overweight you may want to wait until after 10 weeks to order your doppler so that you are not caused any unnecessary worry. Not finding the baby's heartbeat is NOT a sign that something is wrong with your baby. Some people, with extra weight or who have deeper pelvic cavities take a bit longer to find the heartbeat. Most people however, can locate it pretty easily after about 10-12 weeks.

I am having trouble hearing my baby's heartbeat; does that mean something is wrong?

No, not at all. Not finding the heartbeat is NOT a sign that something is wrong with your baby. Sometimes it takes a few tries to get the hang of using a fetal doppler, especially in the first trimester. Make sure that you are using a good amount of gel and place the probe directly on top of the gel (the gel acts as the transuding agent). Please refer to our 'Tips for Successful Doppler Use' manual that you received with your package. If you are still having trouble feel free to call or email us, we are happy to help.

I am hearing two heartbeats; does this mean I am having twins?

No not necessarily. It is very possible to hear the heartbeat in more than one place especially later on in pregnancy. If you are picking up a heartbeat in two locations at roughly the same rate (within 10 bpm or so) then assume its just a single baby's heartbeat in two places. However, if you are picking up a heartbeat in two locations at drastically different beats per minute (ei: one is 130 and one is 160) then that may be more of an indication of twins. The only way to really know if you are having twins though, is through an ultrasound.

What is considered normal for a fetal heart rate?

A normal fetal heart rate is usually between 120 and 180 beats per minute and varies according to fetal age and activity level at the time.
　

How much gel should I use?                                         

You need to use about a quarter sized blob at first, do not rub it into your skin but rather place the probe directly on top of the gel. The gel acts as a transuding agent and will help to give you an accurate heart rate display and good clear sound.