Amniotic Band Syndrome (ABS)

Definition - What does Amniotic Band Syndrome (ABS) mean?

Amniotic band syndrome (ABS) is a variety of congenital abnormalities that develop from the entrapment of pieces of amnion around fetal body parts. Consequences range from malformation of body parts to complete amputation in utero. Treatment involves the postpartum corrective surgical release of bands at 24 weeks. In instances where vital parts are entrapped, in utero correction has been attempted.

Amniotic band syndrome is also known as amniotic band sequence.

FertilitySmarts explains Amniotic Band Syndrome (ABS)

The amniotic sac is a two layer bag made up of the amnion (innermost) layer and the chorion (outermost) layer. These two layers add to the strength of the amniotic sac and in most situations stay intact until labor starts. In ABS, there is a rupture of the amnion that leaves the chorion and thus the sac itself intact. The torn amnion creates thick fibrous bands that become entangled around the fetal body parts. As the fetus grows, the bands become tighter, cutting off blood supply and in some situations, amputating the fetal part.

The exact cause of ABS is unknown but the two leading theories hypothesize that the amnion might rupture from poor blood supply from the placenta, while another theory is that the because there are other co-existing malformations in the fetus besides the bands, for example, cleft lip/palate or club feet, there may be an overall vascular problem with the fetus and the bands are just one of the symptoms.

ABS can be diagnosed in utero via ultrasound with classic symptoms of swelling of the entrapped limbs and as long as there is still detected blood flow in the limb with movement, any surgical corrective treatment is delayed till after birth. With advancements in technology, there have been attempts to cut bands in utero but if the compression is incompatible with life, the mother is given the option to terminate the pregnancy.

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