TRISOMY 21 with NT

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Trisomy 21 with Increased Nuchal Translucency (NT)

Introduction

Trisomy 21, also known as Down syndrome, is a genetic disorder caused by the presence of an extra copy of chromosome 21. It is one of the most common chromosomal abnormalities, affecting approximately 1 in 700 live births. Prenatal screening plays a crucial role in early detection, and increased nuchal translucency (NT) is one of the key ultrasound markers associated with Down syndrome.

Understanding Nuchal Translucency (NT)

Nuchal translucency refers to the fluid-filled space at the back of a fetus’s neck, which can be measured via ultrasound between 11 and 14 weeks of gestation. An increased NT measurement is often associated with chromosomal abnormalities, congenital heart defects, and genetic syndromes, including Trisomy 21.

Normal vs. Increased NT Measurements

  • Normal NT: Typically less than 3.0 mm.
  • Increased NT: Greater than 3.0 mm, which raises suspicion for chromosomal abnormalities.

Trisomy 21 and NT Measurement

Risk Correlation

  • Studies show that an increased NT measurement significantly raises the likelihood of Down syndrome.
  • The combination of NT measurement with maternal age and biochemical 
  • markers (such as free β-hCG and PAPP-A) improves the detection rate.

    • Additional Ultrasound Markers

    Alongside increased NT, other ultrasound findings that may suggest Trisomy 21 include:

    • Absence or hypoplasia of the nasal bone
    • Short femur or humerus length
    • Echogenic bowel
    • Cardiac abnormalities

    Diagnostic Confirmation

    If NT is increased, further diagnostic tests are recommended:

    1. Non-Invasive Prenatal Testing (NIPT): Analyzes cell-free fetal DNA from maternal blood with high sensitivity for Trisomy 21.
    2. Chorionic Villus Sampling (CVS) or Amniocentesis: Definitive diagnostic tests to confirm chromosomal abnormalities.

    Implications and Management

    • If Trisomy 21 is confirmed, parents receive genetic counseling to discuss prognosis and options.
    • Additional fetal echocardiography may be recommended due to the increased risk of congenital heart defects.
    • Multidisciplinary prenatal and postnatal care is crucial to optimize outcomes.

      • Conclusion

      An increased NT measurement is a significant marker for Trisomy 21, but it is not definitive on its own. Combining NT screening with biochemical tests and confirmatory genetic testing provides a comprehensive approach to prenatal diagnosis. Early detection allows for informed decision-making and specialized medical support for affected families.

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