Amniotic band anomalies are a group of birth defects thought to have a common origin in a malfunction of the amnion part of the pregnancy membranes. While the exact mechanism of amniotic band syndrome birth defects is not known for sure, the following is considered the most likely and the most understandable explanation: The amnion is the ‘sack’ that lines the ‘bag of waters’ within the mother’s uterus (womb). It surrounds the developing baby. It is itself part of the pregnancy, formed early on from cells descended from the original fertilized egg.
Normally the amnion lies flat against the wall of the womb, held there by the pressure of the amniotic fluid or ‘waters.’ While the baby brushes up against it during movement, the amnion normally doesn’t bind or affect the baby in any way. In some cases, perhaps because of leakage of the amniotic fluid or for unknown other reasons, the amnion pulls away from the wall of the womb, and fluid collects beneath it, forcing the amnion against the fetus and in some cases affecting the development of the baby.
If a fetal arm or leg is pushed though the amnion, the amnion can pinch off the blood supply to the developing limb, causing it to either grow in a withered fashion or be lost so that it appears to have been amputated. This can happen to any portion of the limb, and the process can involve more than one limb or the head or the torso, though head or torso involvement is extremely rare.
When the torso is involved, abdominal wall defects, (such as omphalocele or gastroschisis), can be seen. When the head is involved, facial clefts and nose or chin abnormalities are the most common. Also, clubbed hands or feet can be seen, as can limb-body complexes where the limb and body are grown together.
Because we do not know for sure what causes this to occur, we likewise do not know how to prevent it from happening. Amniotic band anomalies are thought to be sporadic (not inherited), and they occur in between 1/1000 and 1/5000 pregnancies. They usually only affect one side of the baby, and usually there are no other birth defects or developmental delays (intellectual disabilities) associated with them. Diagnosis before birth is usually made at the time of a routine ultrasound screening in the middle of the pregnancy, but these anomalies can escape detection before birth.
Diagnosis & Treatment of Amniotic Band Birth Defects
Upper or lower limb anomalies or amputations are managed by the Division of Orthopaedics. The clinic meets monthly and works to maximize function and, to the degree possible without limiting function, achieve cosmetic acceptability.
Correction of clubfeet is done in the first months after birth with the non-surgical Ponseti technique, which is so successful that many children so treated as infants have grown up to become famous athletes.
Abdominal wall defects, omphalocele and gastroschisis, can be surgically corrected after birth. The results are generally very good with an expectation of normal function and lifespan.
Facial clefts and chin or nose anomalies are surgically repaired in stages by a multi-disciplinary clinic led by plastic surgeons, again generally with very good results.