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Does Your Baby Have Fetal Heart Arrhythmia ? Causes, Diagnosis, Treatment

It can be frightening to learn that your child has a congenital heart defect. The Fetal Heart Program at the SSM Health Cardinal Glennon St. Louis Fetal Care Institute brings together the best cardiothoracic surgery, cardiology, neonatology and maternal-fetal medicine experts in the region to care for mothers and their babies who have a congenital heart defect. Advances in technology and treatment options at SSM Health allow us to provide the highest quality care for your little one.

What Is Fetal Arrhythmia and How Is it Diagnosed?

Arrhythmias, abnormal or irregular heartbeats, can happen to babies still in the womb. Some types of irregular and abnormal heartbeats are relatively benign and will not affect the baby at all; others can be life-threatening. There are many types:

Tachycardia: The heartbeat is too fast.

Supraventricular Tachycardia: A rapid heart rhythm that begins in the upper chambers of the heart.

Bradycardia: The heartbeat is too slow.

Complete Heart Block: The heartbeat that starts in the atrium does not travel to the ventricle. A person with complete heart block may require a pacemaker. This may happen in fetuses whose mothers have lupus.

Premature Atrial Contractions: The heartbeat originates in a different part of the atrium than it normally would. These often occur in healthy people, have no symptoms, and typically do not cause problems. In rare cases they can cause supraventricular tachycardia.

If your doctor suspects an arrhythmia after reviewing your routine ultrasound, he or she may request a fetal echocardiogram (echo), an ultrasound of the fetal heart. This safe, noninvasive test shows the structure of the heart and helps determine the type of arrhythmia. This can help us confirm the diagnosis and discuss possible options for treatment.

How Is it Monitored and Treated During and After Pregnancy?

Premature heartbeats may have no effect on a fetus. Fetal tachycardia or bradycardia can cause heart failure either in the womb or at birth.

Bradycardia related to complete heart block needs to be closely followed in-utero to watch for development of heart failure.

Supraventricular tachycardia may require treatment before birth, because it can result in heart failure. Typically, mothers are hospitalized and started on medications that help control the fetal heart rate. After delivery, these babies are monitored and may require medication. Our Fetal Heart Team at the Cardinal Glennon St. Louis Fetal Care Institute will monitor your baby closely during pregnancy and help coordinate a delivery plan.

What Is the Long-term Prognosis?

Overall, if treated early, the long-term prognosis for most arrhythmias is good. Babies with tachyarrhythmia may require medication to regulate their heart rates. Some children or adolescents require a minimally invasive procedure to control the arrhythmia. In cases of severe bradycardia, the child may require surgical placement of a pacemaker. Follow-up care with a pediatric cardiologist is crucial to ensure long-term health.

We are here to help – and we’re available 24 hours a day. Call us anytime to schedule an appointment, second opinion, or even if you have a question at (314) 268-4037. Our health care team at the Cardinal Glennon St. Louis Fetal Care Institute strives to provide the best care possible for your child, allowing you to rest assured your little one’s heart is in good hands.

Types of fetal arrhythmias

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 percentTrusted Source 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 percentTrusted Source 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 percentTrusted Source 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 birthsTrusted Source in the United States.

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

Treating fetal arrhythmias

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.

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