What is bradyarrhythmia?

Fetal bradyarrhythmia is an abnormally slow fetal heart rate.

In some cases the slow heartbeat may also have an irregular rhythm.

Bradyarrhythmia is one of several types of fetal cardiac arrhythmias, congenital heart conditions involving an abnormal heartbeat. Arrhythmias can cause the fetal heart to beat too fast, too slow or irregularly.

Bradyarrhythmia is also sometimes referred to as bradycardia.

How does bradyarrhythmia affect my baby?

A normal fetal heart rate is between 110 and 160 beats per minute (bpm). Fetal bradyarrhythmia is generally defined as a sustained heart rate less than 110 beats per minute.

Bradyarrhythmia can range from mild to serious, depending on gestational age, underlying cause, and each baby’s unique condition, including any associated complications.

In mild cases, where no other conditions are present, a slow heart rate may resolve on its own, with no harm to the fetus and no long-term consequences.

In severe cases of sustained low heart rate, bradyarrhythmia can be life-threatening, putting the fetus at risk of non-immune hydrops (excess fluid in multiple areas of the body) and heart failure.

Generally the slower the fetal heart rate, and the earlier it occurs in pregnancy, the worse the outcome for the fetus.

Cause and Prevalence

Fetal arrhythmias as a whole are rare, complicating an estimated 1 to 2 percent of all pregnancies.

A slow fetal heart rate is typically caused by problems with the heart’s electrical system, which sends out electrical impulses that signal the heart muscles to contract or beat. The problem can occur in the sinus node, the heart’s natural pacemaker, where these electrical impulses are generated. Or there may be a problem in the conduction or transmission of the signals from the heart’s upper chambers (atria) to the lower chambers (ventricles). 

In many cases bradyarrhythmia is associated with other conditions, including congenital heart defects, maternal connective tissue disease (lupus), and chromosomal anomalies.

Types of Bradyarrhythmia

There are several types of bradyarrhythmia ranging from mild to serious, including:

  • Sinus bradycardia – a slower than normal heart rate (110 beats per minute or less) with a regular rhythm (meaning the electrical signal still transmits from the upper chambers to the lower chambers of the heart). Sinus bradycardia may be temporary and can occur during an ultrasound exam when pressure is applied to the uterus. In some cases, sudden onset of sinus bradycardia can be a sign of fetal distress, such as fetal hypoxia (lack of oxygen), indicating the need for immediate delivery. In most cases, sinus bradycardia occurs when the sinus node is damaged or not functioning properly, resulting in slow signals to the heart muscles. Mild sinus bradycardia typically needs no treatment, if there are no other abnormalities present.
  • Atrioventricular (AV) block (first-degree heart block) – occurs when the timing of conduction (transmission of electrical impulses) between the upper and lower chambers of the heart is prolonged. Typically no treatment is needed if there are no other abnormalities present.
  • Partial heart block (second-degree heart block) – occurs when the electrical impulses from the upper chambers (atria) are intermittently blocked from reaching the lower chambers (ventricles). These are known as dropped or skipped beats. The result is a slower and sometimes irregular heartbeat. Partial heart block is also referred to as partial atrioventricular (AV) block.
  • Complete heart block (third-degree heart block) – occurs when none of the electrical impulses from the atria reach the ventricles. While another natural pacemaker takes over to generate the electrical signals needed for the ventricles to contract, this can result in a much slower and unreliable heart rate. Complete heart block is the most common cause of a persistent slow fetal heart rate. It is a life-threatening condition, placing the fetus at risk of hydrops and heart failure. The condition is usually associated with either a structural fetal heart defect or with maternal autoimmune disease (such as lupus).


Fetal bradyarrhythmia is typically diagnosed during a routine prenatal ultrasound or when the doctor listens to the fetal heartbeat.

If an abnormally slow heart rate is detected, a comprehensive ultrasound exam should immediately be performed to evaluate fetal well-being, including movement, muscle tone and amniotic fluid level, to determine if the baby is in distress and needs urgent delivery. Maternal blood and urine tests may be performed to screen for maternal conditions that may be causing the slow fetal heart rate.

If fetal bradyarrhythmia is diagnosed, prompt referral to a fetal cardiac center is important for accurate diagnosis of the type of bradyarrhythmia and any associated conditions, ensuring proper treatment.

At Texas Children’s Fetal Center, we arrange for you to visit as quickly as possible for a comprehensive assessment by a team of specialists experienced in fetal arrhythmias, including maternal-fetal medicine (MFM) physicians (OB/GYNs specializing in high-risk pregnancies), fetal and pediatric cardiologists, fetal imaging experts, and pediatric electrophysiologists (specialists in heart rhythm problems).

Additional testing may include:

Our specialists will then meet with you about the results, discuss treatment recommendations, and answer any questions your family has, to help you make the most informed decisions regarding your baby’s care and treatment.

Treatment During Pregnancy

Treatment will depend on the type of bradyarrhythmia, gestational age of the baby, any associated conditions, and the overall health of the fetus and mother.

Your baby’s heart rate and well-being will be closely monitored throughout pregnancy for signs of fetal hydrops and heart failure. 

Treatment strategies may include:

  • Close monitoring only. In mild cases, treatment typically isn’t required but the baby’s heart rate should be monitored in detail until the condition has completely resolved.
  • Medications given to the mother to improve fetal heart rate and neonatal outcomes
  • Steroids if preterm delivery is expected, to promote fetal lung growth
  • Treatment to address any underlying causes
  • Premature or emergency delivery, if needed  


Delivery should take place at a center with the highest quality congenital heart program, ensuring the expertise and resources required to treat fetal arrhythmias during delivery and after birth, including an advanced neonatal or cardiac intensive care unit (NICU or CICU), if needed.

Delivery and postnatal care should be carefully planned and coordinated across a team of maternal-fetal medicine specialists, cardiologists and neonatologists experienced in these rare fetal conditions. In some cases, especially when baby’s well-being is of concern, a caesarean delivery may be advised.

Our fetal center team works closely with the pediatric experts at Texas Children’s Heart Center, for seamless access to the critical care services and specialists your child may need after delivery, avoiding the need for transfers. Here, the heart specialists treating your newborn have been an integral part of their care team since before birth.

Treatment After Birth

Treatment needs after birth vary based on each baby’s arrhythmia and any associated conditions.

In mild cases, the slow heart rate may increase to a normal rate over time without treatment. All babies with bradyarrhythmia should be followed closely until the condition is completely resolved.

In some cases, medications and even a pacemaker may be needed after birth to increase the speed of the heart rate, with life-long care required.  

Your baby’s postnatal care team may include:

Why Texas Children’s Fetal Center?

  • A single location for expert maternal, fetal and pediatric care. At Texas Children’s Hospital, mothers and babies receive the specialized care required for the diagnosis and treatment of congenital heart conditions all in one location, for highly coordinated care and treatment planning.
  • A skilled, experienced team with proven outcomes. We have a dedicated team of maternal-fetal medicine specialists, fetal imaging experts, cardiologists, neonatologists, electrophysiologists and others who work in concert to care for you and your baby every step of the way, using proven protocols we’ve developed over the years. With their combined expertise and unified approach, this team offers the best possible care for pregnancies involving fetal arrhythmias.
  • We care for your child’s needs at every stage of life. Our comprehensive approach starts with your first prenatal visit and continues through delivery, postnatal care, childhood and beyond, as needed, thanks to one of the nation’s leading teams of fetal and pediatric heart specialists.

Texas Children’s – #1 in the Nation for Pediatric Cardiology and Heart Surgery

Our Fetal Cardiology Program is a collaboration between Texas Children’s Fetal Center and Texas Children’s Heart Center, ranked #1 in the nation for pediatric cardiology and heart surgery by U.S. News & World Report, with outcomes among the best in the country.

In the News

Additional Resources

Volumes and Outcomes


Research and Clinical Trials

Texas Children’s, together with our partner institution Baylor College of Medicine, constantly strives to seek new and better treatments for babies with congenital heart conditions.

For more information, please contact the Cardiovascular Clinical Research Core at 832-826-2064 or email sandrea@texaschildrens.org.

Learn more about our fetal cardiology research.

For more information or to schedule an appointment,

call Texas Children’s Fetal Center at 832-822-2229 or 1-877-FetalRx (338-2579) toll-free.

Our phones are answered 24/7. Immediate appointments are often available.