Introduction of NT Screening

NT Screening

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Nuchal translucency (NT) screening is a prenatal test performed during the first trimester of pregnancy, usually between 11 and 14 weeks, to assess the risk of certain chromosomal abnormalities in a fetus, particularly Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome), Trisomy 13 (Patau syndrome) or Turner syndrome (Monosomy X).

How the NT screening works

1. NT screening is most effective when combined with:

• Maternal age.
• Biochemical markers
• Additional ultrasound markers (nasal bone, ductus venosus, tricuspid flow)

2. Ultrasound: An ultrasound is used to measure the thickness of the fluid-filled space at the back of the baby's neck. This is done while the baby is still in the early stages of development.
3. Blood Test: A blood test is often done at the same time to measure the levels of certain substances in the mother's blood (such as free beta-hCG and PAPP-A). These measurements, combined with the NT measurement, help calculate the risk of chromosomal conditions.
4. Risk Assessment: NT screening does not diagnose chromosomal abnormalities but provides a risk assessment based on the fluid measurement, the blood test results, and the mother's age. A higher-than-normal NT measurement can indicate an increased risk, but it does not mean the baby has a condition.
5. Follow-up Tests: If the NT screening shows a higher risk, it may lead to further diagnostic testing, such as amniocentesis or chorionic villus sampling (CVS), which can provide definitive results regarding genetic conditions. The goal is to provide a risk estimate, not a diagnosis, and to help guide decisions for further testing like NIPT or invasive testing.

why NT screening is important?

Nuchal Translucency (NT) screening is important because it is a non-invasive, early screening test used to assess the risk of chromosomal abnormalities and structural anomalies in the fetus during the first trimester of pregnancy (typically between 11 to 13+6 weeks of gestation)
1. Early Detection of Chromosomal Abnormalities

• Measures the fluid-filled space at the back of the fetal neck (NT).
• Increased NT is associated with:
• Trisomy 21 (Down syndrome)
• Trisomy 18 (Edwards syndrome)
• Trisomy 13 (Patau syndrome)
• Turner syndrome (Monosomy X)

2. Identifies Risk for Structural Abnormalities

• Enlarged NT may also indicate:
• Congenital heart defects
• Diaphragmatic hernia
• Body stalk anomaly
• Other syndromic conditions (e.g., Noonan syndrome)

3. Combined with Biochemical Markers

• NT measurement is often combined with:
• Serum markers (PAPP-A, free β-hCG)
• Maternal age
• This combination improves the detection rate (>90%) for Down syndrome with a low false-positive rate (~5%).

4. Safe and Non-Invasive

• NT scan uses standard ultrasound—no radiation or risk to the fetus.
• Provides critical early information without invasive procedures.

5. Guides Further Testing

• Abnormal NT results may prompt:
• Non-invasive prenatal testing (NIPT)
• Fetal echocardiography
• Chorionic villus sampling (CVS) or amniocentesis for genetic diagnosis