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How Does a Fetal Doppler Work?

If you’re pregnant, it’s likely that your whole world is starting to revolve around your baby. You and your partner are looking for new ways to bond with the baby and are consumed with worries about his or her health. You’ve heard about fetal dopplers and how they allow you to hear your baby’s heartbeat at home. You know what a magical experience that would be and it’s tempting to go ahead and purchase one, but you’re skeptical. Your baby’s health is the most important thing to you and before you use a doppler, you need some common questions answered: How does a doppler work? How is it used? Is it even safe?

This guide has you covered. We’ll discuss everything from the history of the baby doppler to frequent concerns a mother may have.

How a Fetal Doppler Works

The technology behind the fetal doppler is based on the “doppler effect.” Christian Doppler, an Austrian mathematician and physicist, discovered that when wave energy travels from two objects, the wavelength can be changed if at least one of those objects are moving. For example, imagine driving and hearing the high pitch sound of a police car directly behind you. However, as the car speeds ahead, the pitch lowers.

Fetal dopplers use this same principle. The fetal doppler’s probe or wand sends out ultrasound waves into the area it is placed over, in this case, the lower belly. These waves are then reflected from the moving object, in this case, the fetal heart. The frequency changes and the doppler then picks up on this change and it transforms it into a sound. The sound can be listened to with speakers or earphones. It will also appear as a heart rate if your fetal doppler has a display screen.

This is what the fetal heart rate sounds like

Although the doppler effect was discovered in 1842, the fetal doppler wasn’t actually invented until over a 100 years later. Dr. Edward H. Hon, a scientist and physician, invented the baby doppler in 1958. A fetal doppler is a handheld device that is used to detect the heartbeat of a fetus inside mother’s womb.

In the past, fetal dopplers were only used by trained doctors and midwives. Now dopplers are available in pocket-sized versions which expectant mothers can use at home without professional supervision. Mothers love listening to the heartbeat with their partners, who are often absent from checkups. It can also help ease their anxiety by reassuring them that their baby is okay.

Are Fetal Dopplers Safe?

Fetal dopplers are safe for both professional and home use and do not require a prescription. All of Baby Doppler’s fetal dopplers are FDA and Health Canada registered. Research does not indicate any risk to the mother or the baby when a fetal doppler is used. In fact, diagnostic ultrasound has been used since the late 1950’s.

The waves emitted by a fetal doppler are many times higher than those emitted from an ultrasound machine. Ultrasound machines also use probes at a much higher frequency, which is why only trained professionals can perform an ultrasound, while anyone can safely use a fetal doppler.

Although fetal dopplers are safe, it’s important to know that they cannot replace regular doctors’ visits. While the fetal doppler can provide reassurance and can help you bond with your baby before birth, it should not be used as medical advice. Any concerns you have should be directed to your doctor or midwife. With an at-home fetal doppler, a midwife can listen to the heartbeat through the phone as well.

What You’ll Need

To listen to your baby’s heartbeat at home, you’ll need a fetal doppler and ultrasound gel.

Fetal Doppler

First off, you will need a fetal doppler, such as the ones available in our store. Our most popular dopplers are the Sonoline B fetal dopplers. Batteries are included, allowing you to get started as soon as you receive the device. The Sonoline B fetal doppler includes an LCD screen that will display your baby’s fetal heart rate (FHR).

Ultrasound Gel

When you purchase one of Baby Doppler’s fetal dopplers, you will also receive a free sample bottle of ultrasound gel. After you receive the doppler, you may run out of the sample quickly. For this reason, we also sell a full bottle of ultrasound gel.

Alternatively, you can also use aloe gel, olive or bio-oil or a lubricant. Some women try to use body lotion; however, it’s not recommended. Regular lotion won’t glide and won’t cut out static as well as a gel.

For best results, we recommend using an ultrasound gel because it will reduce static noise and make cleanup easier.

How Soon Can I Hear the Heartbeat?

Although it is possible for a fetal doppler to detect a heart rate as early as 8 to 10 weeks, it’s recommended that you wait until 12 weeks. After this time, it will be easier to hear the beat. Attempting to hear it before this time may lead you to worry or become impatient.

Every woman and baby is different when it comes to how early a heartbeat can be heard. Here are some factors that play a role in detection:

  • Size of mother’s body (overweight women may have to be more patient to hear the baby’s heartbeat)
  • Position of the fetus. In the early stages of pregnancy, the baby flips in the uterus, which can make the heartbeat difficult to detect.
  • The size of the fetus

How to Use a Fetal Doppler

Lie flat on a sofa, bed or massage table and expose your abdomen. It’s possible to use a fetal doppler while sitting or standing, however lying down will be easiest.

Apply a generous amount of ultrasound gel to your lower belly in one blob; do not spread it around with your hand.

The more gel you use, the less static you will hear. Place the doppler probe in the gel and turn the device on. Start from the pubic bone and slowly glide the probe upwards to your belly button. The fetus may be hard to find at first, so make sure you don’t miss any area of the stomach. Gently and slowly rock the probe until you can see the fetal heart rate displayed on the device’s screen.

What Heart Rate is Normal?

When you first see your baby’s heartbeat on the display screen, you may be startled as it may be higher than you expected. But don’t worry! It’s healthy for a fetal heartbeat to be between 120 and 180 beats per minute. It’s supposed to be a lot higher than a healthy adult’s heart rate, which ranges from 60 to 100. That means if the device detects a heartbeat within this range, it’s likely getting it from your own veins and arteries.

When you listen to your baby’s heartbeat, it will be very quick. Some women compare the sound to galloping horses. If the heartbeat momentarily fades, that is normal; it means your baby is moving around and switching positions.

Why Can’t I Hear a Beat?

Don’t panic if you can’t hear your baby! Just because you can’t hear the fetus does not mean there’s anything wrong. Patience is key. If you’re in your early stages of pregnancy, the baby’s heartbeat may not be strong enough to hear yet. The baby may also be in a position that doesn’t allow the fetal doppler to detect the heart rate. The baby’s heartbeat can also be masked by other noises, such as stomach noises, the mother’s heartbeat or static. The bigger your baby gets, the easier it will be to find the heartbeat.

If you can’t hear the heartbeat, try again in a few minutes or even the next day.

Why Do I hear Two Heartbeats?

Hearing two heartbeats doesn’t necessarily mean that you’re having twins. During the later stages of pregnancy, it is possible to hear the same heartbeat in two places. If both heartbeats are within 10 beats per minute to each other, then it’s likely just one baby. On the other hand, if the two heartbeats are drastically different, you may be having twins. If you weren’t expecting twins, an ultrasound is recommended.

If you are having twins, it may be difficult to distinguish between the two heartbeats.

Tips for Using a Fetal Doppler

  • It’s easier to hear the baby if you have a full bladder. This will help bring your uterus up out of the pelvic cavity.
  • Have a towel nearby to make clean up easier.
  • Some women say it’s easier to hear their baby first thing when they wake up in the morning. This is when the body is least bloated.
  • Avoid build-up on the probe by cleaning it after each use. For best results, switch off the device and wipe the probe with 70% ethanol and let air dry. Alternatively, you can also clean the surface with a clean and dry cloth. Do not submerge the device in water or any cleaning solution.

Using your fetal doppler for the first time? Tweet us or leave us a note on Facebook about your experience. We’d love to hear about it!

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6 thoughts on “How Does a Fetal Doppler Work?

  1. It’s interesting to read about how you can use a fetal doppler and how you can make it easier. I got one of these machines for my wife and to use it effectively I’ll have to make sure we always have her lie down on the couch with a full bladder to ensure we get an accurate reading.

  2. I started using my fetal Doppler at about 10 weeks. I have listened to the baby’s heartbeat everyday since then and I am now 16 weeks. I have just read that it may not be safe, that it could cause brain damage, by heating up tissue of the baby, also hearing problems for the baby. Is this true? There were no indications not to use it daily. In the beginning it would take me about 25-30 minutes to find it and now I find it immediately. Could you please inform me as to the safety of the Doppler for daily use. Has anyone else used it daily?

    1. Hi Stacey, thanks for your comment. The FDA has said that no studies have shown any negative effects to developing babies from fetal Doppler use by the parents to listen to their baby’s heartbeat. FDA has cleared the sale of fetal dopplers for home use but at the same time has issued an advisory to follow your doctor’s instructions for the correct usage of the devices.
      Using fetal dopplers is a safe and effective way for expecting parents to bond with their baby and feel secure while listening to the heart beat.

      If you have any other question don’t hesitate in contacting us at

      Kind Regards,

      Bruna Furlan

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