Fetal Doppler technology has revolutionized prenatal care, allowing expectant parents and healthcare providers to monitor fetal health with exceptional precision. By utilizing ultrasound waves, a fetal Doppler device can detect and amplify the heartbeat of a developing fetus, providing valuable insights into the baby's well-being. This blog will explore the principles behind fetal Doppler technology, its applications, benefits, and considerations for safe and effective use during pregnancy.

What is a doppler fetal monitor?

A Doppler fetal monitor is a handheld ultrasound device that healthcare providers and midwives use from late in the first trimester for routine prenatal care, primarily to listen to a fetal heartbeat using sound waves. While these devices have become available over the counter (OTC) for home use, their use outside medical settings is discouraged due to unknown long-term health effects and the potential for inaccuracies in interpreting fetal well-being.

Why and when Fetal Monitoring is done?

The fetal heart typically begins beating around five to six weeks of gestation and can be detected with a transvaginal ultrasound at that time. However, it takes more time for the heartbeat to strengthen enough to be picked up by a fetal Doppler, usually around 10–12 weeks into pregnancy. Detection timing can vary due to factors like miscalculated due dates, a tilted uterus, or the masking effect of placental sounds or abdominal fat layers. If fetal heart tones aren't audible by 10–12 weeks, it doesn't necessarily indicate a problem, but your healthcare provider may recommend an earlier ultrasound for clarity. Starting in the second trimester, Doppler monitoring at prenatal visits becomes routine to track the baby's heartbeat.

During labour, your baby's heartbeat is monitored in addition to regular prenatal checks. If continuous electronic fetal monitoring isn't in use, healthcare providers such as doctors, midwives, or nurses will intermittently use a fetal Doppler to assess the heart rate. Typically, intermittent monitoring with a Doppler occurs every 15–30 minutes during the first stage of labour and every 5–15 minutes during the second stage. Those experiencing pregnancy complications may require more frequent monitoring to ensure the baby's well-being.

How does doppler fetal monitor work?

A Doppler fetal monitor utilizes ultrasound technology to detect fetal and placental sounds using the Doppler effect, which measures changes in sound wave frequency as the observer moves relative to the sound source. Unlike ultrasound scans that produce images, a fetal Doppler only emits sound. It consists of a probe and a main unit connected by a cord. During use, a healthcare provider applies gel to the probe and moves it across the pregnant person's abdomen to detect fetal sounds, which are heard through the main unit's speaker. Fetal heart rates typically range from 110 to 160 beats per minute and may vary in response to activity or contractions, necessitating regular monitoring during labor. An abnormal heart rate could signal fetal distress, prompting further medical evaluation or intervention.

Fetal heart rate monitoring could happen in your doctor’s office or at the hospital. The procedure will depend on what type of monitoring you’ll have.

External fetal heart rate monitoring procedure:

• Your doctor or technician will instruct you to undress and lie down on an exam table or labor bed.
• They will apply clear gel to your belly.
• Using a device called a Doppler transducer, your doctor will gently press it against your belly and move it around.
• You will hear the sound of your baby’s heartbeat.
• If continuous monitoring is needed, they will secure the transducer with a wide belt.
• The fetal heart rate will be recorded, and you may view it displayed on a computer screen.

Internal fetal heart rate monitoring procedure:

• You will be asked to undress and lie down.
• You will position your feet and legs in supports, similar to a vaginal exam setup.
• The doctor will assess your cervix for dilation.
• If your water has not broken, the doctor may rupture the membranes.
• The doctor will palpate to locate your baby’s head.
• They will insert a thin tube (catheter) with a small wire at the end into your vagina.
• The wire will be placed on your baby’s scalp and the catheter will be removed.
• Once connected to a cable, the wire will continuously record your baby’s heartbeat until it is removed by a doctor, or your baby is born.

Uses & Application of fetal doppler:

Routine Prenatal Care: Healthcare providers use fetal dopplers starting from late first trimester for routine prenatal check-ups to monitor fetal heart tones, typically detectable around 10-12 weeks.

Monitoring Fetal Health: During labour, fetal dopplers intermittently monitor fetal heart rates when continuous electronic fetal monitoring isn't used, typically every 15-30 minutes in the first stage and more frequently in case of complications.

Clinical Applications: Fetal dopplers aid in detecting abnormalities in fetal heart rates, indicating potential issues such as oxygen deficiency, prompting further medical intervention or testing.

Safety and Considerations: Although available for home use, using fetal dopplers without medical supervision is discouraged due to potential misinterpretations and lack of professional guidance.

What are the types of Fetal Heart Rate Monitoring?

External monitoring during pregnancy involves using manual or electronic devices placed on the outside of the abdomen to monitor fetal health:

• Fetoscope: Resembling a stethoscope, a fetoscope has a cone-shaped end that your provider presses against your belly to listen to your baby’s heartbeat, similar to how they listen to your heart and lungs.
• Handheld Doppler ultrasound: This device uses sound waves to measure the baby’s heart rate. Your provider applies gel to your abdomen and places the probe, which picks up the heartbeat and displays it on a screen. While handheld Doppler devices are available for at-home use, the FDA advises against their use without medical supervision.
• Continuous Doppler ultrasound: During labour, continuous electronic fetal monitoring may be used. The ultrasound device is held in place on your belly with an elastic strap, alongside an instrument measuring contraction. Wires from these instruments connect to a monitor providing ongoing monitoring of your baby’s heart rate.

Internal monitoring of fetal heart rate involves attaching a wire directly to the baby's head inside the uterus to monitor heart rate continuously. This method is used less frequently and typically during labor and delivery under specific circumstances:

• After your water has broken
• When external electronic fetal monitoring results are unreliable
• When more precise monitoring is required

Is Fetal Heart Monitoring Safe?

Fetal dopplers are medical devices intended for use by trained professionals in medical settings, where ultrasound, including dopplers, is considered safe during pregnancy. The Food and Drug Administration (FDA) cautions against recreational use of over the counter (OTC) fetal dopplers due to unknown long-term effects. Prolonged or improper use may increase the risk of tissue heating and bubble formation in tissues, potentially posing risks to both the fetus and the user. Moreover, untrained individuals may misinterpret doppler readings, leading to unnecessary anxiety or false reassurance.

What is the risk in Fetal Heart Rate Monitoring?

• Monitoring devices may sometimes indicate abnormalities that do not actually exist, leading to unnecessary interventions or anxiety.
• External monitoring devices like dopplers may provide inaccurate readings if not positioned correctly or if there are technical issues.
• Continuous monitoring can sometimes lead to unnecessary medical interventions, such as cesarean sections, based on interpretations of fetal heart rate patterns.
• Internal monitoring involves inserting a wire into the uterus, which carries a risk of infection or injury to the fetus or mother.
• Despite its widespread use, the precise benefits of continuous fetal heart rate monitoring in improving outcomes for mothers and babies are debated among experts.

How to use an at-home fetal doppler:

• Insert batteries if necessary and ensure the device is ready for use.
• Lie down in a comfortable position, ensuring you have easy access to your lower abdomen.
• Lift your top and lower your pants slightly. Apply a gel suitable for ultrasound (if available) or use alternatives like aloe vera or lotion for lubrication.
• Switch on the doppler and adjust the volume to a comfortable level.
• Move the doppler slowly across your lower belly. Start below your belly button and move around gently until you hear the fetal heartbeat. Note that you may also hear your own heartbeat or the pulse of an artery, but the fetal heartbeat will be much faster.
• Recognize that the fetal heartbeat will typically sound faster than your own heartbeat or pulse.

What does experts have to say about Fetal Heart Rate Monitoring:

At-home fetal dopplers are popular among expectant parents, but they raise safety concerns. In 2014, the FDA advised against their recreational use, recommending their use only when medically necessary under a healthcare provider's supervision. While ultrasound research hasn't shown harm, caution is prudent due to potential tissue heating and microbubble formation in tissues.

Daily use of at-home dopplers is discouraged, as frequent exposure could pose risks. Moreover, relying on doppler readings may lead to false reassurances. A case highlighted in the British Medical Journal underscored this risk when a woman detected a heartbeat but later experienced a stillbirth. This incident emphasizes that dopplers cannot replace professional medical evaluation.

If you notice reduced fetal movements, unusual symptoms like spotting or abdominal pain, do not rely solely on a doppler. Seek immediate medical advice for proper evaluation and care. Always prioritize caution and consult healthcare professionals for any concerns during pregnancy.

Fetal Doppler technology revolutionizes prenatal care by enabling healthcare providers to monitor fetal health through ultrasound detection of heartbeat sounds. Typically used from the second trimester onwards, these devices help track fetal heart rates during routine check-ups and labor. While safe when used by professionals, at-home use is discouraged due to potential misinterpretations and safety concerns highlighted by regulatory bodies like the FDA. It's crucial for expectant parents to rely on medical guidance for accurate monitoring and interpretation of fetal well-being throughout pregnancy.