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Normally, as the foetus grows, the amnion expands and merges with the outer chorion layer. However, if this process is incomplete, the amnion may tear, forming fibrous bands.
These bands can become tangled around parts of the foetus's body, like arms, legs, or fingers, restricting growth and leading to deformities. The severity of ABS ranges from minor issues like small indentations to more severe challenges like missing limbs, constrictions, amputations, or malformations. The extent of the deformities depends on where and how tightly the bands form.
The condition is also known by names like:
- Amnion rupture sequence
- Congenital constricting bands
- Streeter anomaly
- Amniotic band sequence
- Constriction band/rings syndrome
- Amniotic band disruption complex
- ADAM complex (amniotic deformities/adhesions/mutilations)
Understanding ABS helps you prepare for potential outcomes and treatment options if diagnosed.
Causes of Amniotic Band Syndrome
The exact cause of ABS remains unclear and is generally considered a chance event. It is thought to result from an early rupture of the amnion, the inner membrane of the amniotic sac.Important facts about its possible causes include:
- Amniotic rupture: The most widely accepted theory is that the amnion tears. This rupture creates loose, fibrous bands that can wrap around or adhere to the foetus.
- Vascular disruption: It refers to a decrease in blood flow to the developing foetus. This may be linked to external factors such as exposure to misoprostol or undergoing iatrogenic invasive procedures like chorionic villus sampling before 10 weeks of gestation.
- Rare genetic links: Most ABS cases are sporadic, but their occurrence in monozygotic twins suggests a possible genetic component in rare instances.
The cause of the initial amniotic rupture is unknown. However, it is not usually hereditary, meaning it is unlikely to occur in future pregnancies.
Prevalence of Amniotic Band Syndrome
ABS affects around 1 in 1,000 to 1 in 15,000 live births. The incidence is higher in stillbirths, occurring in about 1 in 70 cases. Both male and female infants are equally affected. There is no clear inheritance pattern.Risk Factors for Amniotic Band Syndrome
Below are some of the factors associated with a higher likelihood of ABS.- Living at high altitudes may increase the risk of ABS, possibly due to hypoxia affecting foetal development.
- First-degree relatives of individuals with ABS have a 42.8 times higher risk, and second-degree relatives have a 50.8 times higher risk compared to the general population.
- Being a firstborn child is associated with a higher risk.
- Use of certain drugs like misoprostol during the first trimester is associated with increased risk.
- Foetuses with ABS are more likely to have a non-cephalic presentation at birth.
- Paternal age younger than 29 years is associated with a higher risk of ABS.
Signs and Symptoms of Amniotic Band Syndrome
Symptoms of ABS are grouped into four main categories:- Constriction rings: These are the most common, appearing as tight bands around limbs or fingers/toes, often causing swelling or scarring. They affect at least 80 per cent of cases.
- Limb defects: Bands can lead to partial or complete amputation of fingers, toes, or limbs, syndactyly (fused/webbed fingers), contractures, or fractures. Lower limbs are more commonly affected than upper limbs.
- Craniofacial defects: Less common, these include cleft lip, cleft palate, facial clefts, or encephaloceles, where brain tissue protrudes through openings in the skull.
- Spinal or neural defects: Rare cases involve scoliosis or other spinal abnormalities.
If a band causes amputation before birth, the body often reabsorbs the severed part. As a result, there may be no trace of it at birth.
Diagnosis of Amniotic Band Syndrome
Diagnosing ABS can be challenging due to its varied presentation, especially prenatally. Some of the diagnostic methods include:- Distal limb oedema: Swelling in the limbs, especially the extremities, is a key sign of ABS during prenatal assessments.
- Ultrasound: Major deformities or amputations caused by ABS may be identified as early as the first trimester via ultrasound. The absence of these abnormalities means a diagnosis of ABS cannot be confirmed. However, the amniotic bands themselves are rarely visible, which makes diagnosis challenging in some cases.
- Magnetic resonance imaging (MRI): In some cases, MRI may be used to provide additional details about foetal abnormalities to support the diagnosis.
- Chromosomal microarray analysis: If the diagnosis remains uncertain, chromosomal microarray analysis may be considered to rule out other genetic conditions that could mimic ABS.
Treatment Options for Amniotic Band Syndrome
There are no specific steps you can take to prevent ABS. Its management depends on the severity of the anomalies, as no standard guidelines exist.- Fetoscopic release of amniotic bands: It is a minimally invasive surgery during pregnancy that can release tight bands threatening limbs, helping restore blood flow and reducing damage. Although plastic surgery may still be needed after birth.
- Surgical intervention: After birth, surgery can relieve constriction rings to improve limb function by reducing venous pressure or fix deformities through reconstructive procedures. Urgent surgery is required if vascular compromise is detected, which means reduced or blocked blood flow to the limb.
Children with missing or shortened limbs can use prosthetics. These are custom-made artificial limbs to improve their ability to move and perform everyday tasks.
Potential Complications of Amniotic Band Syndrome
ABS can lead to several complications, like:- Pregnancy loss: The risk of miscarriage/stillbirth increases significantly when vital organs or the umbilical cord are severely affected.
- Preterm birth: ABS is associated with an increased risk of premature delivery.
- Functional impairments: Limb or craniofacial defects can affect mobility, dexterity, or appearance.
FAQs on Amniotic Band Syndrome (ABS)
- How common is Amniotic Band Syndrome?
ABS affects approximately 1 in 1,000 to 1 in 15,000 live births and has a higher incidence in stillbirths. - What are the symptoms of Amniotic Band Syndrome?
Symptoms include constriction rings around limbs, limb defects like amputations, craniofacial defects, and, in rare cases, spinal or neural defects. - How is Amniotic Band Syndrome diagnosed?
It can be diagnosed through prenatal ultrasound, MRI, and chromosomal microarray analysis.
