Amniotic band syndrome is a rare condition caused by strands of the amniotic sac that separate and entangle digits, limbs, or other parts of the fetus. This constriction can cause a variety of problems depending on where strands are located and how tightly they are wrapped.
The developing fetus floats in amniotic fluid in the mother's uterus. What keeps the fluid around the fetus and in the uterus is a sac. This sac has 2 layers which are stuck together: the outermost layer which lines the uterus is called the "chorion", and the layer closer to the fetus is called the "amnion".
It is believed that amniotic band syndrome occurs when the inner membrane (amnion) ruptures, or tears, without injury to the outer membrane (chorion). The developing fetus is still floating in fluid but is then exposed to the floating tissue (bands) from the ruptured amnion. This floating tissue can become entangled around the fetus.
The incidence of amniotic band syndrome is 1 in 1200 to 1 to 15,000 live births. The cause of amnion tearing is uncertain and is consider a chance event. It does not appear to be genetic or hereditary, so the likelihood of it occurring in another pregnancy is remote.
The complications from the amniotic band syndrome can range from mild to severe. In mild cases, a band may become wrapped around digits (fingers or toes) of the fetus. This can result in amputations of the fingers or toes, or syndactyly of the fingers or toes. Syndactyly is a condition where the fingers or toes become fused together, or webbed, which can be treated surgically after birth. Amniotic bands attached to the face or neck can sometimes cause deformities such as cleft lip and palate.
In other instances, a band can be wrapped around a limb (arm or leg) resulting in restriction of movement leading to deformities such as clubbed foot. In more severe cases, an amniotic band can become extremely constrictive leading to decreased blood supply and possible amputation of the limb.
The most severe, and life-threatening complication of amniotic band syndrome is if a band becomes wrapped around vital areas such as the head or umbilical cord. Constriction to the umbilical cord or other vital areas can result in fetal death.
Each case is unique, multiple strands may be entangled around the fetus, and the severity can range from mild to life-threatening depending on where the bands are constricting and how tightly they are wound.
If there is evidence of amniotic bands, a detailed ultrasound test should be done to assess the severity and avoid a misdiagnosis. Amniotic bands can be difficult to detect by ultrasound because of their small size, so it is important to have your case reviewed by someone knowledgeable in amniotic band syndrome. The individual strands are often hard to see on an ultrasound, and typically the condition is detected indirectly by the constrictions and swelling they cause to limbs and other parts of the fetal body.