FETAL DOPPLER

 FETAL DOPPLER

Fetal Doppler is a portable ultrasound tool that uses sound waves to listen to the heartbeat of the fetus. Doctors and midwives begin using these medical devices during the first trimester of pregnancy as part of routine prenatal care.  Recently, the fetal Doppler has been sold over the counter (OTC) for home use. However, its use outside of medical settings is discouraged because the long-term health effects are unclear and its use may lead to inaccurate conclusions about the fetus.

The device is usually battery-powered and has a probe that can slide on the abdomen of pregnant women. With hearing aids, you, your partner, friends or family members will be able to hear your baby's heartbeat. If you are interested in knowing your baby's heart rate, some models are also equipped with an LCD screen.

If you want to know how fetal Doppler works, their technique is based on the "Doppler effect", discovered by Austrian mathematician and physicist Christian Doppler. Simply put, the fetal Doppler probe sends ultrasound to the lower abdomen. These waves are reflected from the fetal heart, and Doppler detects the change in frequency and turns into sound.

Although the home model may be relatively new, fetal Doppler ultrasound has existed since it was invented by doctor and scientist Edward H. Hon in the late 1950s. Since then, they have been mainly used by doctors and midwives.

Since the wave emitted by the fetal Doppler is approximately many times higher than the wave emitted by the ultrasound machine, the device can be used safely at home. In addition, fetal Doppler have been approved by the FDA and Health Canada.

Doppler effect

When scattered particles are unstable in the presence of incident waves, the Doppler effect occurs. The frequency of the incident wave is modified according to the direction of movement of the particles.

Biological tissue is composed of multiple dispersed stationary and moving particles (primarily blood cells). When coherent light from the laser enters tissue, there will be a Doppler frequency shift when it encounters moving particles. Therefore, the tissue backscatter signal can be broken down into flow, cell concentration, and cell rate. There are two common methods for laser Doppler perfusion monitoring: one is to keep the fiber probe (transmitting and receiving fiber) in contact with the skin , and the other is to use a scanning mirror (XY) or beam splitter to transmit light to the skin and The received light is guided to a photodetector to form an image. This method usually achieves an interrogation depth of 1mm , where most of the dermal capillaries and blood vessels are located, and the flow velocity in the range of 0.01 to 0.1mm/s can be determined .

WHEN FETAL DOPPLER IS USED

The fetal heart begins to beat around five to six weeks of pregnancy. Around that time, the fetal heartbeat can be detected by transvaginal ultrasound. However, before the heart sound can be detected by fetal Doppler, the heart sound must become a bit louder.

WORKING PRINCIPLE OF FETAL DOPPLER

In general, Fetal Doppler is an ultrasound which uses the sound waves to detect the sounds of the fetus and placenta. Its name comes from how it works, using the Doppler effect. That is, it detects how frequency waves (sound waves in this case) change as the observer approaches or moves away from the sound source. Unlike ultrasound, fetal Doppler only produces sound, not images. The  Fetal Doppler is composed of a probe and a host, which are connected by a cable. To use the device, the doctor will place the gel on the end of the tube. Then move the gel probe around the exposed abdomen of the pregnant woman until it detects the voice of the fetus.

The sound is heard through the speaker of the main unit. Some Doppler’s display the number of beats on the host, while others require the doctor to manually count them.  Fetal heart sounds are usually in the range of 110 to 160 beats per minute. Heart sounds generally change with activity or contraction, so it is important to monitor fetal heart sounds during labor.  Abnormal heart rate may indicate that the baby is not getting enough oxygen or has other problems. When the heart sound exceeds the expected range, the doctor may recommend further tests or an intervention.

Difference Between Fetal Doppler And Ultrasound

Parents who use fetal Doppler at home may not get as good results as an ultrasound examination in a doctor’s office. On the one hand, if you dress too early or put it in the wrong position, you may not hear your heartbeat and worry. Or you may hear the heartbeat (it may be yours or your pulse) and think that everything is fine, but it is not. In addition, the fetal atomic Doppler mainly captures the baby’s heartbeat (although some companies provide 3D and 4D ultrasound, allowing you to view images and videos of the fetus).

The most common medical ultrasound is transvaginal ultrasound, in which a magic wand (called a transducer) is placed in the vagina to send sound waves and collect information. Another popular ultrasound, trans abdominal ultrasound, is performed by moving the device to your stomach, similar to what is done on a home Doppler.

Professional ultrasound can be used for many purposes. Ultrasound can confirm your pregnancy, determine when you are pregnant, listen to the baby’s heartbeat, and detect any abnormalities in the baby. It can also determine the content of the placenta and amniotic fluid, and even the location of the baby’s birth. Professional fetal Doppler can provide detailed information about the baby’s blood flow.

TIPS FOR FINDING FETAL HEARTBEAT WITH DOPPLER

Sound detection on the fetal Doppler does not necessarily mean that it has detected a heartbeat. In fact, the sound you hear may be that of the placenta or your own arteries. When you first use Doppler, distinguishing between them can be a bit confusing. However, by using these techniques, you should be able to recognize your baby’s heartbeat immediately.

#1 Start Low, Go Slow

If you haven’t heard your baby’s heartbeat, it is best to start from the middle of his pubic bone. When you move upward in a gentle swing, be sure to move slowly. Since it can detect a lot of noise, you don’t want to accidentally hover your mouse over the fetal heartbeat. Although you might think that pressing the tube will force you to “close” to the baby, this is not the case. Fishing it lightly is the best way.

#2 Be Generous with the Gel

During your ultrasound examination, you may have noticed that the technician sprays a lot of gel on your lower abdomen because it makes the test easier. Although you may wish to use gel frugally, it helps reduce static electricity. If you are worried about running out, a whole bottle is very helpful. Don’t rub it on your belly like a moisturizer. Instead, apply the sphere to a spot and use the probe to spread it out.  Some people try to use whatever they have on hand, such as lotion. However, this may produce weaker and more static results. If you need a substitute, aloe vera gel or lubricant is the next best choice.

#3 Use Fetal Heartbeat Monitor on a Full Bladder

If you  can try to plan for bladder filling before using fetal Doppler. This helps lift the uterus out of the pelvis. Therefore, the sound can be clearer and easier to detect.

#4 Use 2MHz Probe if Overweight

One factor in determining how easy it is to detect a heartbeat is the shape of the mother. If a mother is overweight, it’s often more difficult to pick up the correct sound. To make it easier, choosing a model with a 2-2.5MHz probe (or buying a replacement probe). Many standard models come with a 3MHz probe, so make sure to look for that specific feature if you’re a plus sized woman.

#5 Pay Attention to the Heart Rate Range

60-80 beats per minute (bpm)   your own heartbeat

120-180 bpm is your baby’s heartbeat

Note that caffeine, alcohol and nicotine may raise the baby’s heart rate . The heartbeat of fetus is much greater than the heart beat of the mother.

#6 Watch for the Whoosh

Whenever you use Doppler, you will hear various sounds, depending on where it is placed. The “hissing”(whooshing) heartbeat sound usually indicates the placenta or movement. Some people also describe this noise as similar to blowing a tree. This should not be confused with the baby’s heartbeat

FETAL DOPPLER TEST RESULTS

It’s very touching to hear your baby’s heartbeat for the first time. Remember that the heartbeat of babies is much faster than that of adults.  If you are in the first trimester and cannot hear your baby’s heartbeat, don’t worry. It is not until 10-12 weeks before Doppler can reliably detect the baby’s heartbeat. Your doctor may try again at your next visit. Ultrasound may give you better results.

The fetal heart rate is between 110,160 beats per minute and can change 5 to 25 times per minute. Your baby’s heart rate will change based on the condition of your uterus. If the heartbeat is out of range, it may mean that your baby is not getting enough oxygen or has other problems.

If your doctor is concerned about your baby’s heartbeat, he or she may recommend a fetal echocardiogram. This is a safe, non-invasive test that can provide a detailed picture of your baby’s heart. It can be helpful to know if your baby has an irregular heartbeat (or arrhythmia) and what type of arrhythmia to receive appropriate treatment.

TROUBLESHOOTING OVERVIEW

Troubles in fetal Doppler

• No Display on the Screen
•  Abnormal FHR

Troubleshooting

No display on the screen

1. Press and hold the power button for two seconds to turn on. If the screen has no screen or the Doppler cannot turn on, open the battery cover to check whether the  Lithium battery is properly installed or inserted. If there is no battery or the battery is in poor contact with the metal spring, please reinstall them.

 FHR is abnormal

2. There is neither fetal heart sound nor FHR chart, check whether the  Probe position is correct or the angle is correct, check whether the  Ultrasonic glue is correct;

3. The fetal heart sound can be heard, but the fetal heart diagram is messy or sometimes the display is not good, and the probe may be located on the side of the fetus’ abdomen. Adjust the position of the probe.

 4. The fetal heart rate chart shows the abnormal curve  after the pregnant woman accelerates or changes her posture. Due to the change of the position of the fetal heart, the position of the probe deviated from the position of the fetal heart.

 5. The ultrasound gel becomes less when used for a long time, causing the probe to not be used normally. Add ultrasonic gel in time.

6. Sometimes the fetus will turn downward and the fetus will be in position behind the occiput. Since the fetus's back moves towards the mother’s back, it is more difficult to control. Naturally, the probe cannot be moved to the back of the fetus, so it is sometimes best to place the probe below the navel and in the middle of the abdomen.

7. If the display is off and the frequency is high, it means that the probe is not in the best position.

8. If the fetal heart rate is low or inaccurate after menstrual control, there are two main reasons:

•  The pregnant woman moves during the test and the Doppler probe is displaced , so the probe is not in the best position.
• Fetal movement. The detected FCF value is considered invalid.

9. If FHR can be detected during the test, but there is no regular fetal movement heartbeat, you may not have found a suitable position. What is detected at this time is the movement of the pulse or the blood flow of the umbilical cord. If  Still cannot find the best position after careful inspection, the doctor should check further to see if the fetus is in good condition .

Safety concerns with home Doppler

In 2014, the U.S. Food and Drug Administration (FDA) recommended against using a fetal Doppler. The FDA says that the only time you should use Doppler is when your doctor uses it, in which case it is medically necessary.

There is no research showing that ultrasound is harmful, but it is better to be cautious when it comes to your baby's health. As a biomedical engineer at the FDA explained, “Ultrasound can slightly heat tissue, and in some cases, it can also create very small bubbles (cavitation) in certain tissues.”

When it comes to some This is even more worrying in the case of fetal Doppler, because some parents may wish to have a fetal Doppler check every day. Use it for a few minutes once a week and it will not cause any harm to your baby. According to the National Health Service (NHS),

At home Fetal Doppler exams can also be potentially harmful because they can give you a false sense of peace of mind.

Following these lines of thought, in 2009, an article in Trusted Sources from the British Medical Journal pointed to the case of a woman who was 38 weeks pregnant. She noticed that the baby was moving less, but found a heartbeat through fetal Doppler, so she did not seek medical help. She's dead. It may have detected her own heartbeat or placental vibrations.

The author said that although stillbirth may be unavoidable, he cautions all parents that fetal Doppler cannot replace the expertise of your physician.

If you suspect that something is wrong with your baby, for example, if his activity is reduced, if he has abnormal drippings or if he has stomach aches, you cannot rely on fetal Doppler at home to detect your baby. Is it good? If you think there is a problem, see a doctor immediately. Even if there is a problem, the baby may have a pounding heartbeat.