What is a Nuchal Translucency (NT) Scan?

The Nuchal Translucency (NT) Scan is a critical component of first-trimester screening conducted between 11 and 14 weeks of pregnancy. The NT scan is a specialized ultrasound Scan that is done by a trained fetal medicine specialist, to assess the baby’s risk of chromosomal abnormalities, such as Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), or Patau syndrome (Trisomy 13).  By measuring the fluid thickness at the back of the baby's neck, this scan, combined with blood tests, provides a detailed risk profile for genetic conditions.      

Purpose of the NT Scan (First Trimester Screening):

1. Risk Assessment for Genetic Disorders: Combined with maternal blood tests, it calculates the risk of chromosomal abnormalities.
2. Early Identification of Structural Defects: Detects signs of conditions such as heart or skeletal abnormalities.
3. General Assessment of Fetal Development: Confirms gestational age, fetal growth, and overall health.

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Why should you get NT Scans done at Fetal Medicine Clinics?

The NT Scan allows early identification of potential chromosomal or structural issues, enabling informed decision-making and timely medical follow-up. It also offers reassurance about the baby's development at a key stage of pregnancy. It is therefore one of those critical scans that should not be missed.

One must also take care to get this scan done at a Fetal Medicine Clinic rather than an ultrasound centre. This is because Fetal medicine Clinics have both trained fetal Medicine experts and the best Ultrasound Machines and reporting tools that are specifically designed for Gynecology and Obstetrics assessments. 

At Petals Imaging, the First Trimester NT scan is always done by our Fetal medicine experts. This is because Fetal medicine experts are specifically trained in this area of Fetal assessment. They are hence better placed than other sonologists or Radiologists to do this scan.

Learn why Petals Imaging is the best Fetal Medicine Clinic in Kolkata

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Why is an NT scan combined with First-Trimester Screening?

The NT scan is rarely done alone and is prescribed as part of a Combined First-Trimester Screening Test. The FTS combines the Ultrasound Biomarkers with biochemical markers from the mother's blood namely:

• pregnancy-associated plasma protein-A (PAPP-A); and
• free ꞵ-human chorionic gonadotropin (free ꞵhCG).

An accurate measurement of the fetal crown-rump length and the nuchal translucency is required, as well as a maternal venous blood sample taken on the same day as the Ultrasound. This Test tells us if the fetus runs a high risk for Trisomies. A Nuchal Translucency (NT) scan is combined with First-Trimester Screening (FTS) to provide a more comprehensive risk assessment for chromosomal abnormalities, such as Down syndrome (Trisomy 21), Edward syndrome (Trisomy 18), and Patau syndrome (Trisomy 13). Here's why they are integrated:

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1. For Enhanced Accuracy

• The NT scan measures the fluid accumulation at the back of the baby’s neck, while FTS includes blood tests for maternal serum markers:
  • Free beta-hCG: Higher levels can indicate an increased risk of Down syndrome.
  • PAPP-A (Pregnancy-associated plasma protein-A): Lower levels may suggest a higher risk of chromosomal abnormalities.
• Combining ultrasound findings (NT measurement) with blood test results and maternal factors (age, weight, etc.) significantly improves the accuracy of risk calculations compared to any one test alone.

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2. For Early Detection of Genetic Risks

• Timing: Both tests are done between 11 and 14 weeks, allowing early identification of potential genetic risks.
• Why Early? Early detection gives parents more options, such as additional diagnostic tests (e.g., amniocentesis or chorionic villus sampling), or time to prepare emotionally and medically for the pregnancy outcome.

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3. For Identification of Structural and Genetic Issues

• The NT scan can reveal:
  • Increased nuchal translucency: Associated with trisomies and other genetic conditions.
  • Certain congenital heart defects or skeletal abnormalities.
• FTS helps correlate these findings with chromosomal risks.

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4. For Personalized Risk Assessment

• By integrating NT measurement, blood test results, and maternal factors, a personalized risk score is calculated.
• This individualized approach allows targeted follow-up, reducing unnecessary invasive procedures for low-risk pregnancies.

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5. Reassurance or Further Action

• Low risk: Provides reassurance and avoids further testing.
• High risk: Suggests the need for non-invasive prenatal testing (NIPT) or diagnostic procedures, ensuring timely intervention.

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Correlation between NT Scan and Downs Screening:

 

The nuchal translucency (NT) measurement, nasal bone assessment, and Down syndrome screening are interrelated as part of first-trimester screening to assess the risk of chromosomal abnormalities, including Down syndrome (Trisomy 21). Here’s how they correlate:

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Nuchal Translucency (NT) Measurement

• What It Is:
  NT refers to the fluid-filled space at the back of the baby’s neck, measured via ultrasound between 11 and 14 weeks of pregnancy.
• Significance in Down Syndrome:
  Increased NT thickness is associated with a higher risk of chromosomal abnormalities, including Down syndrome. It may also indicate heart defects or other genetic conditions.

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Nasal Bone (NB) Length

• What It Is:
  The nasal bone is assessed during the same first-trimester scan. The absence or underdevelopment of the nasal bone is a marker for Down syndrome.
• Significance in Down Syndrome:
  Babies with Down syndrome often have a smaller or absent nasal bone compared to those without chromosomal abnormalities.

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Correlation in Downs Screening

1. Combined Role:
   • NT measurement and nasal bone assessment are used together in first-trimester screening to calculate the likelihood of Down syndrome when combined with maternal age, blood markers (like free beta-hCG and PAPP-A), and sometimes uterine Doppler measurements.
   • A higher NT or absent nasal bone increases the calculated risk.
2. Statistical Association:
   • Studies show that about 60–70% of babies with Down syndrome have an absent nasal bone on ultrasound in the first trimester.
   • Increased NT, combined with an absent or short nasal bone, significantly raises the suspicion of chromosomal anomalies.
3. Diagnostic Follow-Up:
   • If NT and nasal bone findings are concerning, the doctor may recommend additional tests like non-invasive prenatal testing (NIPT) or invasive procedures (e.g., chorionic villus sampling or amniocentesis) for definitive diagnosis.

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Importance of Both Markers in Screening

• Neither NT nor nasal bone findings alone are diagnostic of Down syndrome but serve as risk indicators.
• They are part of a multi-factorial approach, and their findings guide further testing or reassurance.

By using these markers together, clinicians can provide a more accurate risk assessment for Down syndrome and other chromosomal conditions.

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