Amniotic Band Syndrome

The term amniotic band syndrome (or amniotic band constriction) describes a congenital deformity caused by the entanglement of a fetus in a web of fibrous tissue strands extending from the lining of the amnion, the innermost layer of the amniotic sac in which the fetus grows into a baby.

In some cases these strands of tissue can wrap themselves around the baby’s limbs and interfere with blood flow, causing swelling or even amputation. In other instances they may attach themselves to the baby’s face, causing facial disfigurement in the form of a cleft lip or cleft palate. This condition is rare, affecting only one out of every 12,000 to 15,000 pregnancies.

Complications Associated with Amniotic Band Syndrome

The degree of danger presented by this condition depends upon its severity—i.e., what parts of the fetus have been ensnared and how badly they are constricted. As noted above, it is possible for limbs or digits to be damaged or even amputated in utero if the bands are wrapped tightly enough. Amniotic bands wrapped around a leg can restrict movement in a way that can cause the baby to be born with a clubfoot.

Another possibility is that the bands may injure the fingers or toes, and that these digits may fuse together as they heal, a condition known as acrosyndactyly. Fusion of fingers or toes can also occur because amniotic bands have bound them together. Digits that do not actually fuse together may still be webbed.

In the worst cases, the amniotic bands may wrap themselves around the umbilical cord, or around the baby’s neck; this is a life-threatening situation that can result in miscarriage or stillbirth. Bands that attach themselves to a fetus’ head may cause a condition known as encephalocele, in which the baby’s skull forms without closing completely, leaving the brain exposed.

Fortunately, most cases are mild, although the prognosis for milder cases, while less frightening, is still gloomy. Permanent indentations and scars are likely to appear where the bands have attached themselves to the baby’s skin. While arms and legs that have been constricted are seldom amputated, there is often some loss of function.

Causes of Amniotic Band Syndrome

The exact cause of this condition is unclear and probably varies from case to case. In general, it is believed to result from any trauma that causes a rupture of tear in the amnion but does not damage the chorion (the outer layer of the amniotic sac). When such an injury occurs, bands of tissue that have separated from the amnion begin to float around in the amniotic sac, where they can attach themselves to the fetus and wrap around limbs, digits, etc.

In most cases the trauma that might cause amniotic band syndrome (ABS) would likely be the result of an abdominal injury, although the National Institutes of Health has suggested that ABS can sometimes occur as a complication of amniocentesis.

Although ABS results in congenital deformity, it is not genetic in nature, nor is it believed to be caused by anything an expectant mother does or fails to do. This means that even if this condition occurs in your pregnancy, it is very unlikely to happen a second time. ABS is an accidental occurrence that has nothing to do with the mother’s anatomy or genetic makeup.

Diagnosing Amniotic Band Syndrome

Diagnosis of this condition is difficult because the amniotic bands are so small that they are difficult to see on an ultrasound. The constriction of the limbs can be seen with ultrasound, however, which may lead a doctor to suspect ABS. Because this condition can be observed only indirectly by ultrasound, a doctor in such a case may want to refer the patient to a specialist who is knowledgeable about amniotic band constriction.

Treatment and Prevention of Amniotic Band Syndrome

There are no known preventative measures that can be taken for ABS. If the condition is not severe it may not require treatment of any kind. In mild cases of ABS there may be visible marks on the baby’s skin after birth, but nothing medically worrisome that would justify an expensive and dangerous surgical intervention.

If treatment is required (such as surgery to correct a cleft lip, or therapy for a circulatory problem) it will often be administered after the baby is born. ABS generally does not complicate delivery or affect the choice of delivery method (i.e., C-sections are rarely necessary).

If the ABS appears to be threatening the baby’s life, however, or if it appears likely that a limb will be amputated, then surgery may be considered. The patient will be given a spinal block or an epidural rather than general anesthesia, and a tiny camera will be inserted into the amniotic sac through her abdomen. The surgeon will cut the amniotic bands, releasing the affected limb, umbilical cord, or other affected body part.

Prognosis for Amniotic Band Syndrome

Most cases of ABS are not severe enough to threaten the life of the fetus, although there may be cosmetic issues that need to be addressed after birth.

This page was last updated on 06/2017

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