Placenta | Amniotic band syndrome (ABS)
Amniotic bands are caused by damage to one of the membrane layers of the placenta called the amnion. Damage to the amnion may produce fibre-like bands, which can trap or constrict parts of the developing baby. They can cause a number of different anomalies, depending on which body part(s) are involved.
- Amniotic band syndrome (ABS) can be mild or can be very serious.
- The findings in ABS depend on the severity and location of the constrictions.
- The mildest constrictions may affect only the skin and do not require any treatment.
- More extensive bands can cause constrictions which may block lymphatic vessels and impair blood flow.
- When the bands affect the limbs, the furthest ends of the limbs are most often involved, especially the fingers.
The commonly accepted view is that ABS occurs when the inner membrane (amnion) breaks or tears (ruptures) without injury to the outer membrane (chorion). This exposes the fetus to fibrous sticky tissue (bands) from the ruptured amnion, which float in the amniotic fluid, and may entangle the fetus.
Amniotic bands may result in additional abnormalities, such as underdevelopment of a limb, bony abnormalities, amputations, leg-length discrepancy and club feet. If the band is across the face it can cause cleft lip and palate. Extensive bands affecting vital organs may be life-threatening. If a band wraps tightly around a limb, constricting its blood supply, the limb or digit(s) may be completely amputated.
On ultrasound, the bands appear as thin, mobile threads, which may be seen attached to or surrounding the baby. However, these bands may be difficult to detect by ultrasound, and may only be diagnosed when the end results are noted at birth, such as missing or deformed limbs.
The majority of cases are mild and require no treatment.
In-utero surgical division of constriction bands, either by fetoscopy or ultrasound guided laser or direct division can lead to improvement in blood flow and prevention of amputation. Complications of these procedures include preterm premature rupture of membranes (PPROM) and premature labour.
Postnatal treatment options include plastic surgery to enhance function or for cosmetic purposes, and prosthesis and physiotherapy for individuals with limb defects.