A nuchal translucency (NT) ultrasound test is very important for pregnant mothers, as it helps determine if the developing baby is growing normally. Many mothers wonder, “Is an NT measurement of 2.5mm normal?” or “What if the NT is 3mm?” Read the information below to find the most accurate answers.
1. What Is Nuchal Translucency (NT)?
Nuchal translucency refers to the fluid collection under the skin at the back of a baby’s neck during the first trimester. On the ultrasound, this area appears as a black or translucent space. If the fetus has certain chromosomal abnormalities, genetic syndromes, or heart problems, the nuchal translucency measurement can be higher than normal.
When an NT scan suggests a higher risk of Down syndrome or other genetic problems, the doctor may recommend additional tests such as amniocentesis or chorionic villus sampling (CVS).
Experts advise that pregnant mothers should have the NT scan between the 11th and 13th week of pregnancy.
2. What Is Considered a Normal NT Measurement?
When having an NT ultrasound, many mothers feel confused about what is normal. Is 3.2mm normal? Is 2.5mm normal? Is 3mm a concern? Below are some reference values:
- At 11 weeks: The NT is usually less than 2mm.
- At 12 weeks: The NT is usually less than 2.5mm.
- At 13 weeks: The NT is usually less than 2.8mm.
- If the fetus is between 45-84mm in length, the NT should be less than 3.5mm.
- If the NT is under 1.3mm, the risk of Down syndrome is very low.
- If the NT is more than 3mm, the risk of Down syndrome is higher.
- If the NT is 6mm, there is a high risk of Down syndrome and some other birth defects.
- If the NT is between 3.2 - 3.5mm, there is a risk of chromosomal abnormalities.
(See more: Does an NT of 1.3mm affect anything?)
3. At What NT Measurement Is There a Risk of Down Syndrome?
The NT scan is usually done during the first trimester (11-13 weeks). The result helps doctors identify the risk of Down syndrome. Generally, the thicker the NT, the higher the risk of Down syndrome and other defects.
- If the NT is over 3mm, the doctor may recommend amniocentesis for a more accurate diagnosis.
- If the NT is between 3.5 - 4.4mm, the chance of a chromosomal abnormality is about 21.1%.
- If the NT is ≥6.5 mm, the chance of a chromosomal abnormality is about 64.5%, meaning a very high risk of Down syndrome.
4. Factors Used to Determine Risk of Abnormalities
When the doctor performs the NT scan, they consider:
- The mother’s age
- The baby’s NT measurement
- The baby’s gestational age
- The mother’s blood test results
- The presence or absence of the baby’s nasal bone
Usually, the standard average risk is about 1 in 300. If the risk is lower (like 1 in 1,000), it’s considered low risk. If it’s higher (like 1 in 100), it’s considered high risk.
Remember, these measurements are just screening indicators, not a definite diagnosis. A high NT measurement does not guarantee the baby will have Down syndrome, and a normal measurement does not ensure the baby is completely free of chromosomal issues.
Statistics show that about 5% of mothers have a high-risk NT measurement, but most babies are born healthy and normal.
In conclusion, the NT scan is one of the important tests to determine if the baby has a risk of Down syndrome. Thanks to modern ultrasound technology and well-trained doctors, the accuracy of NT measurements is very high. Hopefully, after reading this, mothers will understand better what is considered normal, such as whether 3.2mm or 2.5mm is normal, or if 3mm is a problem. It’s also important to choose a reliable medical facility for the NT scan of your baby.
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