What is a NT ultrasound scan?

A nuchal translucency (NT) ultrasound scan is a prenatal screening test conducted during the first trimester of pregnancy, typically between 11 and 14 weeks of gestation. The primary purpose of the NT scan is to assess the risk of certain chromosomal abnormalities, such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13).

During the NT scan, an ultrasound is used to measure the clear (translucent) space in the tissue at the back of the baby's neck. Babies with certain chromosomal abnormalities tend to accumulate more fluid at the back of their neck during the first trimester, which increases the size of this clear space.

How the NT Scan Works:

1. Measurement: The sonographer measures the nuchal translucency using ultrasound.
2. Additional Factors: The results of the NT scan are often combined with other factors, such as the mother's age and blood test results (if part of a combined screening), to estimate the risk of chromosomal abnormalities.
3. Results: The measurements and factors are used to calculate a risk ratio (e.g., 1 in 1,000) indicating the likelihood of the baby having a chromosomal abnormality.

Benefits:

• Non-Invasive: The NT scan is a non-invasive test that poses no risk to the mother or the baby.
• Early Detection: It allows for early detection and assessment of potential chromosomal abnormalities.

Limitations:

• Screening, Not Diagnostic: The NT scan is a screening test, not a diagnostic one. A high-risk result doesn't mean the baby definitely has a chromosomal abnormality; further diagnostic tests (such as chorionic villus sampling (CVS) or amniocentesis) would be needed for confirmation.
• Accuracy: The test provides a risk assessment, not a definitive answer. There are possibilities of false positives and false negatives