Amniotic Band Syndrome (ABS)

Amniotic band syndrome (ABS) occurs when the lining of the amniotic sac is damaged during pregnancy, creating fibrous, string-like strands of tissue that entangle the fetus or parts of the fetus and or umbilical cord. Called amniotic bands, these strands may wrap around different parts of the developing body, restricting blood flow and disrupting the baby’s normal growth.

What is Amniotic Band Syndrome (ABS)?

Amniotic band syndrome (ABS) occurs when the lining of the amniotic sac is damaged during pregnancy, creating fibrous, string-like strands of tissue that entangle the fetus or parts of the fetus and or umbilical cord.

Called amniotic bands, these strands may wrap around different parts of the developing body, restricting blood flow and disrupting the baby’s normal growth. The compression causes a wide range of birth defects, from mild deformities to severe malformations, loss of limbs, or life-threatening complications.

ABS is also known as amniotic band disruption, amniotic band sequence, constriction ring syndrome and adhesion and mutilation (ADAM) complex, among many other names.

The congenital disorder is rare, affecting anywhere from 1 in 1,200 to 15,000 live births.

How Does ABS Affect my Baby?

The presence and severity of birth defects depend on where the amniotic bands are located and how tightly they are wrapped. The bands most commonly constrict the limbs, fingers and toes, but they can also wrap around the fetus’s head, neck, umbilical cord or vital organs. 

Some babies experience nothing more than a skin indentation, while others may be born with clubbed feet, fused fingers or toes, a cleft palate, abdominal wall defects or other physical deformities. In the most serious cases, severe constriction can result in congenital or intrauterine amputation (missing limbs, fingers, or toes), debilitating facial/skull clefts, and neural tube like defects such as an encephalocele or a potentially fatal obstructed blood supply if the baby’s umbilical cord is involved.

 

What Causes Amniotic Band Syndrome?

The precise cause of ABS is unknown, although researchers do not believe it is genetic or hereditary. A widely accepted theory however, concludes it occurs when the lining of the amniotic sac is torn or ruptured during the earlier stages of pregnancy (prior to 20 weeks gestation).

How is Amniotic Band Syndrome Diagnosed?

ABS is usually diagnosed at birth, since the amniotic bands are difficult to see on a routine ultrasound. In some cases, however, abnormalities such as limb malformations are visible.

If the condition is suspected, your physician may refer you to a fetal center for a comprehensive evaluation and or order additional testing, including:

  • Anatomy ultrasound: a high-resolution ultrasound to confirm the diagnosis and assess for other anomalies. The ultrasound can help determine where the bands are located, and evaluate blood flow with Doppler flow studies as necessary.
  • Fetal MRI: a non-invasive imaging technique to help provide additional details of the baby’s organs that may not have been visualized on ultrasound. The fetal MRI can assess the severity of constriction and abnormalities.  
  • Fetal echocardiogram: a specialized ultrasound to evaluate the baby’s heart structure and function
  • Amniocentesis: A medical procedure in which a small sample of the amniotic fluid that surrounds the baby in the womb is extracted and studied in the lab and tested for genetic abnormalities. The results could affect the treatment and overall outcomes.  Also, amniocentesis can be used to confirm results of screening using cell-free fetal DNA. 
  • Cell-Free Fetal DNA: Your doctor can take a sample of your blood to look for copies of fetal (baby) DNA.  This is only a screening test. A positive result means that there could be problems with the DNA.  This should be confirmed with another test to be sure of the result.  

These procedures provide more detailed images and information about your baby’s condition.

How is ABS Monitored and Treated?

Once ABS is diagnosed, your doctors will closely monitor your pregnancy as well as your baby’s growth and development. Regular ultrasounds will help to identify changes, risks and possible complications while allowing you and your medical team to develop a plan of care.

Mild birth defects may not need treatment. Other cases will require medical and/or surgical intervention, which is usually performed after the baby is born.  

Postnatal treatments include:

  • Surgery: Babies may need surgery immediately following delivery or later in life. When necessary, emergency surgery is performed to release the constricting bands. Plastic and reconstructive surgery to repair deformities may be delayed for months or even years, allowing the baby time to grow.
  • Physical and/or Occupational Therapy: Some infants will need rehabilitative therapies to increase strength and function. The type of therapy depends on the type of birth defect.
  • Prosthetics: Children who have lost a limb may be candidates for a prothesis. 3-D printing and other advances have vastly improved these devices, allowing children to regain limb function as early as 12 to 18 months of age.

Sometimes, however, ABS causes severe or life-threatening damage that must be addressed before the baby is born. For example, an amniotic band may be wrapped around the umbilical cord or is cutting off the blood supply to a limb. In these cases, fetal surgery may be an option.

A minimally invasive procedure called fetoscopic amniotic band resection is commonly performed when in utero intervention is necessary. This procedure may be necessary in life threatening conditions, such as when the baby’s umbilical cord is being constricted or more commonly, when a limb or digits is at risk of being amputated by the constriction. With the help of ultrasound-guided imaging, a specialized surgeon utilizes a tiny instrument (with a camera on the tip) to reach the fetus through the mother’s abdomen and cut the band or bands, releasing constriction and preventing further harm, such as loss of life or limbs.

It is important, however, to consider that amniotic band resection carries serious risks, including premature delivery, bleeding and damage to the fetus, before making an informed decision.

 

How Will ABS Affect the Long-term Health of my Baby?

Long-term outcomes vary, generally depending on the body parts affected and the severity of the condition.

The best outcomes are typically associated with cases that involve the limbs, when resulting birth defects often can be surgically repaired or addressed with interventions that restore function and do not impact overall health. In the most extreme cases, ABS can cause permanent or life-threating abnormalities.