More recently, fetal dopplers have been sold over the counter (OTC) for at-home use. Use outside of medical settings is discouraged, however, because the long-term health effects are unknown and its use may lead to inaccurate conclusions about the fetus.
When It Is Used
The fetal heart begins beating around five to six weeks’ gestation. Around that time, a fetal heartbeat may be detected with a transvaginal ultrasound. The heart sounds need to get quite a bit stronger, however, before they can be detected with a fetal doppler.
During Pregnancy
Fetal heart tones can be detected by a fetal doppler usually around 10–12 weeks in pregnancy. Every pregnancy and body is different, so detection can happen slightly earlier or later than that window.
Your healthcare provider may attempt to pick up heart tones using the fetal doppler as early as 10 weeks, although you shouldn’t worry if they aren’t audible yet. Although heart tones not picked up by around 10–12 weeks could indicate a problem, this is not always the case.
Some reasons fetal heart tones may not be detected early on in pregnancy include:
Your due date was miscalculated, and you are not as far along as you thought you were. You have a tilted uterus, which makes it more difficult to detect fetal heart tones. Your placental sounds overpower the fainter sounds of the fetal heartbeat. The layers of fat in your abdomen act as a barrier to the quieter, early fetal heart tones. You are using an at-home doppler.
If your healthcare provider or midwife has difficulty obtaining fetal heart tones, especially if you are close to 12 weeks, they may recommend an ultrasound, which is able to find heart activity much earlier—often as early as five or six weeks.
Beginning in the second trimester, your healthcare provider will begin using the fetal doppler at every prenatal visit to check your baby’s heartbeat.
During Labor
In addition to being checked during prenatal visits, your baby’s heartbeat will also be assessed throughout labor. If you are not being continuously monitored with an electronic fetal monitor, your doctor, midwife, nurse or other healthcare provider may intermittently check your baby’s heart rate with a fetal doppler.
Intermittent monitoring with a doppler is usually done every 15–30 minutes during the first stage of labor and every 5–15 minutes in the second stage. People experiencing pregnancy complications are monitored more frequently.
How It Works
A fetal doppler is a type of ultrasound that uses sound waves to detect fetal and placental sounds. It gets its name from how it works, using the Doppler effect. That is, it detects how waves of frequency—in this case sound waves—change as the observer moves toward or away from the source of the sound. Unlike an ultrasound scan, a fetal doppler only produces sound, not an image.
Fetal dopplers are made up of two parts—the probe and the main unit—connected by a cord. To use the device, a healthcare provider will place gel on the end of the probe. The gelled probe is then moved around a pregnant person’s bare abdomen until it detects fetal sounds.
Sounds are audible through the speaker on the main unit. Some dopplers display the number of heartbeats on the main unit, while others require the practitioner to count them manually.
Fetal heart tones typically fall between 110 and 160 beats per minute. Often heart tones change in response to activity or contractions, which is why it’s important to monitor fetal heart tones during labor.
An abnormal heart rate could indicate that the fetus is not getting enough oxygen or is having other problems. When heart tones fall outside of the expected range, a healthcare provider may recommend further testing or intervention.
Types
Some dopplers are made to be waterproof so that a user can submerge the probe in the water. These dopplers are particularly useful when a person is laboring in water.
Dopplers come in a variety of strengths, measured in megahertz (MHz). MHz is defined as one million cycles per second. Fetal dopplers used in healthcare provider’s offices and sold for OTC use are usually 2 MHz or 3 MHz. For comparison, a probe used for a transvaginal ultrasound can be as high as 5 MHz.
Other Devices
Fetal dopplers are the most common tool used by healthcare providers for listening to the fetal heartbeat because they are the most sensitive and the most convenient. But the doppler isn’t the only device that can be used to hear your baby’s heartbeat. Here are some others:
Stethoscope Fetoscope Pinard horn Fetal monitor
Is It Safe?
Fetal dopplers are medical devices that are designed for use by medical professionals. When used by trained professionals in a medical setting, ultrasound, including fetal dopplers, is considered safe for use during pregnancy.
While there is currently no evidence of harm from doppler use, the Food and Drug Administration (FDA) advises against using an OTC fetal doppler recreationally because the effects of repetitive use are unknown.
Ultrasound can heat and produce small bubbles in tissues. When exposure is increased, such as with repetitive at-home use, the potential for harm to the fetus and the parent increases. Also, when an untrained person uses a doppler, readings from the device may be misinterpreted, causing unnecessary alarm or a false sense of security.
A Word From Verywell
A fetal doppler is a reliable tool for health professionals to listen to a fetus’s heartbeat during pregnancy and in labor.
While it may be tempting to purchase an OTC fetal doppler so that you can listen to your baby’s heartbeat, it’s important to remember that the FDA advises against this because of the potential risk that repeated use may pose to your baby and to you. Doppler use by laypeople also can result in unnecessary alarm or false reassurance.
There are alternative devices for listening to your baby’s heartbeat. You should talk to your healthcare provider or midwife if you have concerns about using a fetal doppler or if you are thinking about using one at home.
In addition, using a fetal doppler without training can cause additional anxiety for the mother. At times, it may be difficult to find a heartbeat, which can cause unnecessary worry and stress.
