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When you’re pregnant, it can be scary to hear your baby has an arrhythmia. But what does this actually mean?

An arrhythmia is an irregular heart rate — too fast, too slow, or otherwise outside the norm. Your doctor may discover this anomaly when doing a routine ultrasound or listening to your baby’s heart with a Doppler device.

Most fetal arrhythmias are benign. However, your doctor may want to monitor your baby closely because some types may indicate a heart defect. Without treatment, these conditions may lead to a buildup of fluid in your baby’s body/tissues (hydrops fetalis), preterm delivery, or even death.

Hearing your little one’s heartbeat is special. You may notice it’s faster than your own. In fact, a normal fetal heart rate is anywhere between 110 and 160 beats per minute. (It’s also important to note that fetal heart rates can change, and they’re also variable from beat to beat.)

When a baby’s heart rate is slower or faster than this — or has some other issue, like skipping beats — it may indicate there’s an issue, like a heart defect, that needs more monitoring.

Fetal arrhythmias are detected in around 2 percent of pregnancies. You may be at higher risk if you:

  • have autoantibodies to Ro/SSA and La/SSB, which are found in people with certain autoimmune diseases, like lupus or Sjögren’s disease
  • have phenylketonuria
  • have preexisting diabetes or gestational diabetes
  • had a fetal heart block in previous pregnancy
  • take teratogenic medications or drugs
  • had infections in the first trimester, such as rubella, parvovirus b19, or cytomegalovirus
  • had a fetal abnormality detected on an ultrasound
  • became pregnant through in vitro fertilization
  • are pregnant with monochorionic twins (identical twins sharing a placenta)

Your baby may also be at a higher risk of heart defects if there’s a family history or if they have a chromosomal abnormality, such as Down syndrome, Turner syndrome, or trisomies 13 and 18. In cases where a first-degree relative (mom, dad, or sibling) has a heart defect, there’s a three-fold increase in the risk that a baby may have a heart defect as well.

Fetal arrhythmias may not always be caused by a structural heart defect, though. Instead, they may be caused by things like inflammation or electrolyte imbalances. Sometimes the cause may even be unknown.

If your doctor suspects your baby has an arrhythmia, you may be sent for more detailed imaging called a fetal echocardiogram. An echo helps to visualize the structures of the heart, blood flow, and other features to help with diagnosis.

This test is noninvasive and is generally done as an abdominal ultrasound by a trained sonographer. Fetal echos can be performed as early as 12 weeks into pregnancy but are more reliable after the 17- to 18-week mark.

The images from the echo are looked over by a pediatric cardiologist. If the results are abnormal, you may be referred to a maternal-fetal medicine specialist for additional monitoring throughout your pregnancy.

There are a number of different fetal arrhythmias. It can be overwhelming researching them on your own — ask your doctor to explain your baby’s to you so you understand what’s going on and what part of the heart is affected. The most common types you may encounter include the following:

Extrasystoles or premature contractions (PCs)

Premature contractions are the most common type of arrhythmia that’s found in the second and third trimesters of pregnancy. With PCs, your baby has extra heartbeats that can either originate in the atria (premature atrial contractions or PACs) or the ventricles (PVCs).

PACs or PVCs that occur in isolation may not require any kind of treatment and may actually resolve on their own before your baby is born. That said, 2 to 3 percent of cases may lead to supraventricular tachycardia (SVT).


When a baby’s heart rate is over 160 beats per minute, it’s called tachycardia. When this happens more persistently, it’s called sustained tachycardia, which occurs more than 50 percent of the time. A heart rate that is too fast may lead to hydrops, heart failure, or polyhydramnios (too much amniotic fluid).

Of all tachyarrhythmias, atrial flutter and SVT — heart rate between 220 and 300 beats per minute — are the most common types you may see.


When a baby’s heart rate is under 110 beats per minute, it’s called bradycardia. To be classified as sustained bradycardia, your baby’s heart rate must remain low for 10 minutes or more when monitored.

Shorter periods of slow heart rate are called transient fetal decelerations and may be benign, especially in the second trimester. Around 30 percent of sustained bradycardia cases will resolve without treatment before delivery.

Atrioventricular blocks

Congenital heart blocks are also called atrioventricular blocks — and there are different degrees. For example, a complete block that causes a dangerous drop in the heart rate is present in around 1 in 20,000 births in the United States.

Heart blocks are caused by either a congenital heart defect or through exposure to maternal anti-Ro/SSA antibodies, as with neonatal lupus.

Not all fetal arrhythmias require special treatment. If your doctor detects an irregular heart rate at your appointment, you may be referred to a specialist to monitor your baby’s heart through the rest of your pregnancy. If things are stable or improve on their own, no further treatment may be necessary.

For issues that require treatment, the treatment will depend on:

  • the cause
  • your health
  • your baby’s health
  • how far along you are in your pregnancy

Your doctor may choose to treat your baby while they’re still inside the womb with medications or in some cases, surgery. Or — again — you may have close monitoring to watch the progress. With a complete heart block, for example, doctors may treat it by giving you steroids or medications like hydroxychloroquine.

Your doctor can best explain the course of treatment and monitoring as it applies to your case directly. Each baby, each pregnancy, and each heart issue is unique, and any treatment you receive will take this into account.

Most fetal arrhythmias are benign and may resolve on their own before delivery. And transient arrhythmias — those that come and go — are more common than sustained arrhythmias, ones that are present always or more often than not.

The Centers for Disease Control and Prevention (CDC) report that around 1 percent of babies (40,000) are born with congenital heart defects each year in the United States. Issues like sustained tachycardia and persistent bradycardia may lead to hydrops fetalis, preterm birth, or death if left undetected or untreated.

The good news is that many cases of heart rhythm issues that are treated early have positive outcomes. And babies who are treated in the womb may not need any special support or medication after birth or beyond the newborn period.

Speak with your doctor if you have concerns about your baby’s heart rate or if you have any risk factors for congenital heart defects.

If your doctor detects an arrhythmia, keep up with your prenatal appointments and any specialist appointments or additional testing, like fetal echocardiograms. Additional monitoring allows your doctor to keep an eye on your baby and develop a treatment plan for during or after pregnancy, if necessary.