One of the most exciting times for pregnancy is the routine ultrasound that is usually performed around the 18th week of pregnancy when physicians check fetal growth, perhaps check the sex of the baby, and count all the fingers and toes. For a very few women, the scan may detect something a little more serious – a condition called amniotic band syndrome, or ABS.
Amniotic constriction bands are strands of fluid-filled sacs that surround a baby in the womb. They are caused by a tearing of the inner part of the placenta called the amnion, which produces the fiber-like bands that may trap the baby’s extremities such as the arms, legs, fingers or toes. As the baby grows, the bands constrict or tighten, they cause a reduction in blood supply and they may develop abnormally or become amputated. In more serious cases, the band may cause an abnormal gap in the face, called a cleft, or cause a defect in the abdomen or chest wall. The most severe cases occur if the band becomes wrapped around the head or umbilical cord, which can result in fetal death.
Other names for the condition include Streeter dysplasia, congenital constriction bands or rings, or amniotic deformity adhesions mutilations (ADAM).
Amniotic banding affects approximately 1 in 1,200 to 1 in 15,000 live births. It is also believed to be the cause of about 178 in 10,000 miscarriages. About 80% of cases involve the hands and fingers and a significant number of clubfoot cases are correlated with ABS.
The timing of the rupture is believed to occur between 28 days after conception to 18 weeks of gestation. Late bands can occur and present at birth, even after a normal ultrasound was performed earlier in the pregnancy. The cause is generally unknown. It most often happens spontaneously, but can also occur if the woman experiences trauma to the lower abdomen.
If diagnosed in utero, rare because the individual strands are small and difficult to see, a higher level 3D ultrasound or MRI may be used for a more detailed and accurate diagnosis. Most often, the baby will be monitored throughout the remainder of the pregnancy, particularly if the bands are not in danger of amputating a limb or causing significant deformity. In these cases, fetal surgery, called amniotic band release surgery, may be considered.
After birth, plastic or reconstructive surgery for the infant will be considered, depending upon the extent of the deformity. Other therapies, such as physical or occupational therapy, would also be considered.
Amniotic band syndrome is considered a chance event and does not appear to be hereditary, except in the case of Ehlers-Danlos syndrome (EDS), a connective tissue disorder. The cause of the amnion tearing is often unknown and there are no preventative measures a mother-to-be can take to prevent its occurrence.
Resources for this article include the University of California San Francisco Fetal Treatment Center