ABS is a group of rare congenital abnormalities that is caused by strands of the amniotic membrane attaching and tangling up with the fetus. Depending on the location and severity, amniotic bands can constrict limbs causing amputations, fuse hands and feet causing webbing of fingers and toes, and constrict other portions of the body causing severe defects.
The cause of ABS is unknown. During pregnancy, there are two linings to the pregnancy sac that holds the fetus and fluid. The outer layer is called the chorion and the inner layer is called the amnion. Amniotic bands are thought to occur when the inner amniotic membrane ruptures or tears without injury to the outer layer. The strands of torn amniotic membrane float in the fluid and become tangled up with the fetus.
The severity and complications of ABS present in a wide range. Bands wrapped around fingers or toes of the fetus can result in amputations or fusions (syndactyly) of those digits. Clubbed feet can result from bands on the foot. Severe constriction around arms and legs can cause major amputations. Bands that wrap around the face can cause deformities such as cleft lip or palate. These conditions are treated after the baby is born.
In more severe cases, bands can cause defects in the abdominal or chest wall or cause constriction of the blood vessels for vital organs. ABS can be life-threatening if the bands wrap around the umbilical cord or the neck.
It is unclear how often ABS occurs as it is difficult to diagnose. Best estimates suggest that ABS occurs in approximately 1 in 1,200 to 15,000 live births.
How is ABS diagnosed?
ABS is very difficult to diagnose. Prenatal ultrasound may not be able to identify the bands but only see the results of the fusion such as missing or deformed limbs.
What will happen during pregnancy?
If ABS is suspected, a detailed ultrasound will be performed to detect the presence of anomalies. In some cases a fetal echocardiogram to examine your baby's heart may be recommended.
Will a fetal treatment be required?
Fetal treatment for ABS is rarely necessary. In certain conditions, amniotic bands may need to be cut during pregnancy if they are wrapped around the umbilical cord or threaten to amputate a limb. If it is determined that fetal intervention is the best option for your baby, your team at the Center will develop a comprehensive plan for you and your baby.
Cutting the amniotic bands is performed utilizing a fetoscopic technique. A small camera is inserted through the mother's abdomen and uterus into the amniotic sac in order to see and cut the bands. The procedure is typically performed under regional anesthesia. Afterwards, you will be admitted to the Women's Center at Children's Memorial Hermann Hospital to monitor for complications. After discharge, you will continue to be followed by the Center and your obstetrician for ongoing care.
What special considerations should be made for delivery?
Type of delivery - Typically, pregnancies with ABS do not require cesarean delivery. The need for fetal intervention should not impact your mode of delivery. The delivery plan will be carefully discussed with you and your obstetrician.
Place of delivery - If all the prenatal monitoring suggests that your baby is doing well, the baby can be delivered at the hospital of your choice. However, the hospital should be prepared to handle any immediate needs of your newborn and have a neonatal intensive care unit with the capability to provide specialized care.
Time of delivery - Unless there are signs of serious complications of ABS, there is no reason to intentionally induce an early delivery. The team at the Center may recommend early delivery for pregnancies that appear to be in danger.
What will happen at birth?
Immediately following delivery, doctors will carefully evaluate and begin treatment if necessary. You and your loved ones should be able to immediately hold and bond with your newborn. If needed, the baby will be stabilized in an intensive care unit and treated by the neonatologists, specialists in high-risk newborns.
What are the long-term outcomes and considerations?
A baby with ABS may need treatment after birth. Most of the complications of ABS are not life-threatening and may be treated on an elective basis. Depending on the complications, some babies may need corrective surgery in order to improve cosmetic features or functionality of hands and feet. These conditions are typically treated by pediatric orthopedic and plastic surgeons. Your team at the Center will develop a comprehensive treatment plan and introduce you to the specialists that treat these conditions.
Contact the Texas Fetal Center to make an appointment with a high-risk pregnancy doctor.
Note: This information regarding your condition is meant to be a helpful, informative introduction. Because every newborn is different, this may not be applicable to all cases, especially if there are additional defects. Your team of experts at the Center will provide you with information specific to your pregnancy.