Amniotic band syndrome is a condition that occurs when the inner layer of the amniotic sac, called the amnion, is damaged during pregnancy, creating fibrous, string-like strands of tissue that entangle the fetus. These strands, called amniotic bands, may wrap around different parts of the developing body, constricting blood flow and keeping the baby from growing normally. The exact cause of the syndrome is not known, but it is not believed to be hereditary. It is considered a chance event and does not appear to be genetic or hereditary, and is unlikely to occur in a subsequent pregnancy. Some experts believe that ABS is the result of circulation (blood flow) problems in the fetus, while others think it is caused by the tearing of the amniotic sac. The presence and severity of birth defects depend on where the amniotic bands are located and how tightly they are wrapped. The bands most commonly constrict the limbs, fingers, and toes, but they can also wrap around the fetuss head, neck, umbilical cord, or vital organs. In rare cases, a healthcare provider may remove amniotic banding with surgery when the fetus is still in the uterus.