Fetal Atrioventricular (AV) Block: Risks Associated with Maternal Anti-Ro/La Antibodies

The risk of fetal AV block in mothers positive for Anti-Ro/La antibodies arises from transplacental autoantibodies damaging the fetal conduction system. This condition most commonly presents as congenital complete heart block and is usually detected between the 18th and 24th weeks of pregnancy. Early diagnosis is critically important for fetal prognosis.

In pregnancies positive for Anti-Ro and Anti-La antibodies, the risk of congenital heart block is approximately 1–2%; if there is a history of a previously affected fetus, this rate increases. Autoantibodies may cause inflammation and fibrosis in the fetal atrioventricular node, leading to permanent conduction defects. Risk assessment should be performed in a multidisciplinary manner.

The mechanism of fetal congenital AV block development is associated with immune-mediated injury and may cause irreversible fibrotic changes. Second- and third-degree block patterns carry risks of bradycardia, hydrops fetalis, and intrauterine loss. The clinical course depends on the degree of block and accompanying cardiac dysfunction.

Monitoring of Anti-Ro/La antibodies and fetal echocardiography during pregnancy should be performed regularly starting from the 16th week. PR interval and heart rate are evaluated with weekly or biweekly fetal echocardiography. In high-risk cases, maternal treatment options and delivery planning are determined by perinatology specialists.

What Are Anti-Ro and Anti-La Antibodies?

Anti-Ro (SSA) and Anti-La (SSB) are autoantibodies directed against ribonucleoprotein complexes found in the cell nucleus and cytoplasm. In the autoimmune process, the immune system perceives its own cellular structures as foreign and produces antibodies against these structures.

During pregnancy, these antibodies can cross the placenta. Especially from the 12th–16th weeks of pregnancy onward, maternal IgG-class antibodies reach the fetal circulation. Anti-Ro/La antibodies may bind to cells in the fetal cardiac conduction system and create an inflammatory response. This condition may lead to fibrosis (scar tissue formation) in the heart and permanent damage to the conduction system.

What Is Fetal AV Block?

Atrioventricular block is the slowing or complete interruption of electrical conduction between the atria and ventricles of the heart. When it develops during the fetal period, it is generally referred to as congenital heart block.

AV block is examined in three degrees:

• 1st-degree AV block: Conduction is delayed but not completely interrupted.
• 2nd-degree AV block: Some electrical impulses cannot reach the ventricles.
• 3rd-degree (complete) AV block: The atria and ventricles function independently from each other. This condition may lead to severe bradycardia (low heart rate). Pacemaker implantation may be required.

Anti-Ro/La-associated fetal AV block is mostly 3rd degree and permanent. This condition is considered the cardiac form of the neonatal lupus spectrum.

Risk Rate and Who Is at Higher Risk?

The risk of developing fetal AV block in Anti-Ro-positive pregnancies is generally around 1–2%. The risk may increase slightly when Anti-La antibodies are also present. In mothers who have previously delivered a baby with Anti-Ro/La-associated congenital heart block, the recurrence risk increases significantly (reported to be approximately 15–20%).

Factors that may contribute to increased risk include:

• High antibody titer
• Presence of active autoimmune disease
• History of neonatal lupus in a previous pregnancy
• Other accompanying autoimmune markers

However, it should be particularly emphasized that fetal heart block does not develop in every antibody-positive pregnancy. Most Anti-Ro/La-positive pregnancies result in healthy outcomes.

Pathophysiology: How Is the Fetal Heart Affected?

Anti-Ro/La antibodies are thought to bind to L-type calcium channels and conduction system cells in fetal cardiac tissue. As a result of this binding:

1. Inflammation develops,
2. Macrophage activation increases,
3. Apoptosis (programmed cell death) is triggered,
4. Ultimately, fibrotic tissue forms.

Once fibrosis develops, the conduction system may be permanently damaged. The atrioventricular node (AV node) and His-Purkinje system are particularly affected. Therefore, complete AV block is generally irreversible.

Diagnostic Process and Monitoring During Pregnancy

Anti-Ro/La positivity is generally detected through blood tests performed in the expectant mother. In women diagnosed with autoimmune diseases, these antibodies may be evaluated before pregnancy planning.

The main recommended approach in high-risk pregnancies:

• Regular fetal echocardiography follow-up between the 16th and 26th weeks of pregnancy
• Weekly or biweekly evaluation of fetal heart rate and PR interval
• Close monitoring for fetal bradycardia

Fetal echocardiography is an ultrasonographic method that provides structural and functional evaluation of the heart. Prolongation in AV conduction time can be detected early.

The expectant mother may not have any symptoms. Therefore, regular follow-up is critically important. Further evaluation is required if the fetal heart rate is detected below 110 beats/minute.

Treatment Approaches

When fetal AV block develops, the treatment approach varies according to the degree of block and the gestational week. However, an important point here is that 3rd-degree AV block is often irreversible.

General principles are as follows:

• In 1st- or 2nd-degree block, maternal corticosteroid treatment may be considered in some centers.
• If there are signs of fetal heart failure, supportive treatments may be planned.
• In the postnatal period, babies with permanent complete AV block may require a pacemaker.

Treatment decisions should be made by a multidisciplinary team. Joint evaluation by perinatology, pediatric cardiology, and rheumatology specialists is important.

No treatment option is standard for every patient. Clinical decisions are based on individual risk assessment.

Evaluation of the Mother

Some women positive for Anti-Ro/La antibodies may have an undiagnosed autoimmune disease. If the following symptoms occur during or after pregnancy, rheumatologic evaluation may be required:

• Dry mouth and eyes
• Joint pain and swelling
• Skin rashes
• Unexplained fatigue

Therefore, in addition to fetal risk, the long-term health of the mother should also be considered.

When Is Specialist Evaluation Required?

Further evaluation is recommended in the following situations:

• Detection of Anti-Ro/La positivity
• Previous history of congenital heart block
• Suspicion of fetal bradycardia
• Findings of fetal hydrops

Early and regular follow-up ensures timely recognition of possible complications.

Prof. Dr. İbrahim Cansaran TANIDIR

Prof. Dr. İbrahim Cansaran Tanıdır is an internationally recognized specialist with nearly 20 years of clinical, academic, and interventional experience in the fields of congenital heart diseases, pediatric interventional cardiology, hybrid procedures, and radiation-reduced / fluoroscopy-free catheterization techniques.

To date, he has performed more than 10,000 pediatric cardiac catheterization procedures both in Turkey and abroad, and has pioneered advanced interventional and hybrid applications in complex structural heart diseases in our country.

His academic productivity represents a scientifically strong authority with 110 SCI/SCIE publications, 1,440 citations, and an H-index of 18 (Google Scholar, 2025).