An arrhythmia is a term used to describe any abnormal or irregular heartbeat. This includes a heart rate that is faster or slower than expected.

Babies can be diagnosed with arrhythmia before they are born. This is known as fetal arrhythmia. A fetal arrhythmia may be diagnosed when a developing baby’s heart rate falls outside the normal range of 120 to 180 beats per minute (BPM).

There are two types of fetal arrhythmias:

Fetal arrhythmia is rare. It is often temporary and harmless. For some babies, however, fetal arrhythmia may require treatment.

Fetal Arrhythmia Causes

The heart has its own electrical system. This system determines how fast the heart beats. Fetal arrhythmia is caused by abnormalities or interruptions in the heart’s electrical system.

Fetal arrhythmia type (tachycardia or bradycardia) is determined by the location of the electrical system’s abnormality or interruption.

Other causes of fetal arrhythmia include:

  • Congenital (present at birth) heart defects
  • Electrolyte imbalances
  • Inflammation
  • Restricted blood flow

Some studies have linked caffeine and fetal arrhythmia. Fetal arrhythmia and anxiety in pregnant women have also been linked.

Fetal Arrhythmia Ultrasound

When a doctor suspects an irregular fetal heart rate, they may order a fetal echocardiogram. This imaging test is sometimes called an “echo.” A fetal echocardiogram is a special ultrasound exam of a baby’s heart.

This noninvasive imaging test allows doctors to see and hear a baby’s developing heart.

A specially trained pediatric cardiologist reviews fetal echocardiogram images to diagnose a fetal arrhythmia and recommend treatment.

Fetal Arrhythmia Treatment

Many fetal arrhythmias resolve on their own and don’t require treatment. Other babies may need regular monitoring and treatment, especially if their arrhythmia affects blood flow. Reduced blood flow to the fetus can affect how much oxygen they receive.

The most common treatment for fetal arrhythmia is medication. These medications are given to pregnant mothers and pass to the fetus through the placenta.

Irregular Rhythms with Normal Heart Rate

Sometimes, doctors hear “extra” heartbeats when listening to fetal heart rate. These extra beats are caused by early (premature) contractions of the heart’s upper (atrial) or lower (ventricle) chambers.

These irregular heart rhythms—though often harmless—should be monitored, as they can lead to other fetal arrhythmias.

Premature Atrial Contractions (PAC)

A premature atrial contraction is an extra beat in the heart’s upper chambers. A PAC disrupts the normal heart rhythm of the fetus, causing an irregular heart rhythm.

Some may refer to PAC as a “skipped beat.”

A PAC may send an electrical signal to the heart’s lower chambers (ventricle). This is called a conducted PAC. A PAC that doesn’t send a signal to the ventricle is called a non-conducted PAC. Non-conducted PACs result in bradycardia.

Non-conducted PACs are the most common type of fetal arrhythmias. These usually resolve without treatment and cause no harm to the fetus. The cause of PACs is unknown in most cases. Doctors will perform an electrocardiogram (EKG) if they hear an irregular heartbeat after birth.

Premature Ventricular Contractions (PVC)

A premature ventricular contraction is an extra beat in the heart’s lower chambers. A PVC disrupts the normal heart rhythm of the fetus, causing an irregular heart rhythm.

A PVC may also be referred to as a “skipped beat.” PVCs are less common than PACs. They usually resolve without treatment or harm. The cause of PVCs is unknown in most cases. Doctors will perform an electrocardiogram (EKG) if they hear an irregular heartbeat after birth.