Fetal Heart Rate Monitoring: What Does It Tell?

Medically Reviewed by Jabeen Begum, MD on December 18, 2023
Written by Lisa Fields
9 min read

Fetal heart rate monitoring is a process that lets your doctor see how fast your baby’s heart is beating. If you’re pregnant, your doctor will want to make sure your baby is healthy and growing. One of the ways they do that is to check the rate and rhythm of your baby’s heartbeat.

The doctor is most likely to do this later in your pregnancy and when you’re in labor. They may combine it with other tests for a closer look if you have diabetes, high blood pressure, or any condition that could cause problems for you and your baby.

The doctor is more likely to use fetal heart rate monitoring when your pregnancy is high-risk. You may need fetal heart rate monitoring when:

  • You have diabetes.
  • You’re taking medicine for preterm labor.
  • Your baby isn’t growing or developing normally.

The doctor might also use a fetal heart rate monitor to make sure your baby is OK when you’re in labor or if there are other reasons to check your baby’s heart rate.

The doctor can monitor your baby’s heartbeat in a couple of ways. They can listen for or electronically record the beats from outside your belly (external fetal monitoring). Or once your water has broken and you’re in labor, they can thread a thin wire through your cervix and attach it to your baby’s head (internal fetal monitoring).

External fetal monitoring

Auscultation: If your pregnancy is going normally, the doctor likely will check your baby’s heart rate from time to time with a special stethoscope (called a fetoscope) or a hand-held device called a Doppler ultrasound. Doctors sometimes call this type of baby heart rate monitoring auscultation.

If you need it, the doctor might do a special test called a nonstress test, usually starting around week 32 of your pregnancy. It counts the number of times your baby’s heart speeds up during a 20-minute period.

For the test, you'll lie down with an electronic sensor belt around your belly that continuously records the baby's heartbeat.

The doctor also may wrap an electronic sensor belt around you to measure the baby’s heart rate during labor and delivery. This lets them know if the contractions are stressing your baby. If so, you might have to have your baby as soon as possible.

Fetal Doppler: A fetal Doppler is a test that uses sound waves to check your baby’s heartbeat. It’s a type of ultrasound that uses a handheld device to detect changes in movement that are translated as sound. 

Most women first hear their baby's heartbeat during a routine checkup that uses the fetal Doppler. Many ultrasound machines also allow the heartbeat to be heard even before it can be heard with a Doppler. You usually get an ultrasound before 12 weeks.

A fetal Doppler test normally takes place during your second trimester (weeks 13 to 28 of pregnancy). Some manufacturers of at-home fetal Dopplers say you may be able to hear your baby’s heartbeat as early as 8-12 weeks of pregnancy. But professional sonographers say that they wouldn’t try to listen to a baby’s heartbeat before 13 weeks because your womb is in your pelvis during the first trimester, and so the device won’t work correctly. Some at-home devices say not to use it before 16 weeks.

If you’re trying to hear your baby’s heartbeat at home, it may be best to first wait for your doctor to check it during one of your prenatal checkups. This is especially true if you’ve been pregnant for less than 12 weeks, to avoid undue concern. It’s a good idea to talk to your doctor before you buy an at-home fetal Doppler. They can talk to you about the benefits and risks involved with using these devices.

Internal fetal monitoring

Once your water breaks and your cervix opens to prepare for birth, the doctor can run a wire called an electrode through it and into your womb. The wire attaches to your baby’s head and connects to a monitor. This gives a better reading than listening to your baby’s heartbeat from the outside.

A fetoscope or fetal stethoscope is a stethoscope specially designed to make internal sounds louder. It looks like a typical stethoscope, but the end is shaped like a bell and is placed on your stomach to listen to your baby's heartbeat. It doesn't require any special machinery or batteries to use, but an experienced doctor or midwife would know what to listen for. A normal fetal heart rate is about twice that of an adult. A fetoscope can also determine a baby's position as the heartbeat will be loudest over the baby's heart.

The Doppler uses soundwaves to determine blood circulation in the baby, uterus, and placenta. The sound you hear comes from the heart valves moving.

Both fetoscopes and Dopplers are available to buy for home use. Many people feel that the fetoscope is better for home use because it doesn't send soundwaves or heat in the baby's direction. The FDA has determined that ultrasound is safe for babies, but this approval was given before 1993, when the FDA allowed an eight-fold increase in ultrasound intensity for fetal examinations. This doesn't mean that ultrasounds are routinely given at the highest intensity, though.

But the FDA, the British Medical Ultrasound Society, the American Institute of Ultrasound in Medicine, and many doctors have spoken out against the use of Dopplers at home because of potential for misunderstanding. Due to a lack of training, you might be falsely reassured about a baby's heartbeat or unable to hear one and panic. Also, no study has been done on the excessive use of ultrasound on fetuses. The FDA notes that using them too much – without medical supervision – could pose risks to your baby’s development.

Using a fetoscope doesn't carry any sort of technological risk, but again, you might misunderstand the heartbeat you hear (or don't hear).

 

 

External monitoring isn’t risky. It doesn’t hurt or use radiation. If your doctor uses a belt, it might be a little uncomfortable. It also might mean you have to stay in bed during labor.

Internal monitoring risks include:

  • Slight discomfort
  • Infection
  • Bruising or scratching your baby’s scalp

If you’re HIV-positive, you shouldn’t have internal fetal heart rate monitoring. That’s because there’s a risk of passing the infection to your baby. If you have other health conditions, ask your doctor if there are any special risks.

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 ask you to undress and lie down on an exam table or labor bed.
  • They'll spread clear gel on your belly.
  • Your doctor will press a gadget called a Doppler transducer to your belly and move it around.
  • You’ll hear the sound of your baby’s heartbeat.
  • If your doctor wants to measure the heartbeat continuously, they’ll use a wide belt to hold the transducer in place.
  • Your doctor will record the fetal heart rate. You may see it on a computer screen.

Internal fetal heart rate monitoring procedure

  • You’ll be asked to undress and lie down.
  • You’ll put your feet and legs in supports, like you’re getting a vaginal exam.
  • The doctor will check to see if your cervix is dilated.
  • If your water hasn’t broken, the doctor may break it.
  • The doctor will feel for your baby’s head.
  • They'll put a thin tube (catheter) with a small wire at the end into your vagina.
  • The doctor will put the wire on your baby’s scalp and remove the catheter.
  • Once it’s connected to a cable, the wire will record your baby’s heartbeat until a doctor removes it or your baby is born.

Clinical fetal Doppler test

If you go to your doctor’s office or clinic, you'll lie down and a technician will hold a small probe against your belly that makes sound waves. Technicians will ask you to stay still while this is going on. The sound waves will then be sent back to an amplifier where they can be heard. The procedure is safe and painless.

At-home fetal Doppler test

This should be used only if there is a medical need. The FDA does recognize that Dopplers can create bonding between parents and unborn babies, but it suggests parents can get this feeling from sessions in the doctor’s office.

Doing a fetal Doppler test at home may not run as smoothly as one done in your doctor’s office, either. You may need to watch some videos online to see how to do it correctly. At-home devices vary from brand to brand, so it’s important to read any instructions and recommendations that come with the packaging. Some mothers find it’s easier to find the fetal heart rate when they do the test with a full bladder.

Bottom line: Talk to your doctor before buying or using an at-home device.

A healthy baby’s heart usually beats 110-160 times a minute in the womb. It speeds up when the baby moves. Signs of possible problems include:

  • Heart beats slower than 110 beats a minute
  • Heart beats faster than 160 beats a minute
  • A heartbeat pattern that isn’t normal
  • The heartbeat doesn’t go up when the baby moves or during contractions

Lack of a normal heartbeat doesn’t always mean something is wrong with your baby. But it can be a sign that the baby isn’t getting enough oxygen.

Your results also may be less accurate if:

  • You’re obese.
  • You or your baby is in the wrong position.
  • You have too much amniotic fluid.

Hearing your baby's heartbeat for the first time can be deeply moving. Keep in mind that a baby's heartbeat is much faster than an adult's.

If you're in your first trimester and you can't hear your baby's heartbeat, don't worry. Dopplers can't reliably detect a baby's heartbeat until 10-12 weeks. Your doctor may try again on your next visit. An ultrasound may give you better results.

A fetal heart rate is between 110 and 160 beats per minute and can vary by five to 25 beats per minute. Your baby’s heart rate can change based on conditions in your uterus. If the heartbeat is outside of the range, it could mean that your baby isn’t getting enough oxygen or has another issue.

If your doctor is concerned about your baby’s heartbeat, they may recommend a fetal echocardiogram. This is a safe, noninvasive test and gives a detailed picture of your baby’s heart. It can help see if and what kind of irregular heartbeat (or arrhythmia) your baby may have so it can get the right treatment.

If your baby’s heart rate isn't what it should be, the doctor may try:

  • Changing your positions to move the baby
  • Giving you fluids through an IV
  • Having you breathe extra oxygen
  • Relaxing your uterus with medicine to slow contractions
  • Giving you other drugs

If these steps don’t return your baby’s heart rate to normal, you may need to deliver them right away. If your cervix is completely open, the doctor may use a tool called forceps or a special vacuum to help you push the baby out. Otherwise, you’ll have the baby by emergency cesarean section.

Your doctor is more likely to use fetal heart rate monitoring during a high-risk pregnancy. Options for monitoring externally include the fetoscope or Doppler ultrasound. Once your water breaks and you’re in labor, your doctor can thread a thin wire through your cervix and attach it to your baby’s head to monitor the heartbeat internally.

When does a fetus have a heartbeat?

By the fifth week of pregnancy, the fetus (usually called an embryo by doctors at this stage) begins to have cardiac activity, though it's coming from a tube-shaped structure rather than a four-chambered heart. The heart continues to develop over the next 4-6 weeks. You often can't hear the heartbeat on ultrasound reliably before 12 weeks.

What week do you monitor a fetal heart?

You usually get an ultrasound before or around 12 weeks to confirm pregnancy (by detecting a fetal heartbeat). You'll get a second ultrasound (fetal Doppler test) around week 20 to check that your baby's heart is beating normally, among other things. If your pregnancy is proceeding without complications, you may not have any more ultrasounds.