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Birla Fertility & IVF
Birla Fertility & IVF

Everything You Need to Know About NT NB Scan

  • Published on September 06, 2022
Everything You Need to Know About NT NB Scan

Discovering you’re pregnant is a joyous moment but it also prompts important health considerations. Prenatal screening, like the NT NB scan, is essential for monitoring the health of both mother and baby. This screening helps detect potential chromosomal abnormalities early in pregnancy, allowing for timely intervention and informed decision-making. By undergoing the NT NB scan, expecting mothers gain valuable insights into their baby’s development

What is the NT NB Scan?

An NT/NB, nuchal translucency/nasal bone scan, detects the chromosomal abnormalities in the foetus by measuring the fluid-filled space behind the baby’s neck. Once the doctor has the exact measurements, they can estimate if your baby has a risk of having any chromosomal abnormalities like Down syndrome.

It’s important to perform this scan during the first trimester of the pregnancy, as the clear space at the back of the baby’s neck starts disappearing after 15 weeks. Along with nuchal translucency, the scan also assesses the thickness of the nuchal fold and checks for the presence of a nasal bone, which can indicate other congenital disabilities like Edwards’ syndrome, Patau syndrome, skeletal defects, heart defects, etc.

Accuracy of the NT NB Scan in Pregnancy

The NT NB scan has an accuracy rate of approximately 70%, which can be significantly improved when combined with other first-trimester prenatal screening tests. It’s essential to perform the scan before 14 weeks, as the accuracy decreases if done later due to the closure of the nuchal space.

NT NB Scan Results

The normal range for NT/NB  measurement during the first trimester of pregnancy is 1.6 to 2.4 mm. This scan is usually performed between 11 to 14 weeks of pregnancy. However, it is said that the results of the NT NB scan are most accurate when obtained before 14 weeks of pregnancy.

A nuchal translucency measurement of less than 3.5 mm is considered normal, while a measurement of 6 mm or higher may indicate chromosomal abnormalities like Down syndrome or other heart defects

How is the NT NB Scan Performed?

For the NT NB scan, the expert will begin by taking an abdominal ultrasound to produce an image of the inside of your body. This will help in measuring the nuchal translucency and factor in other details like the mother’s age and due date to assess the risk of fetal abnormalities.

Typically, the scan takes less than 30 minutes, during which you are expected to lie on your back on the examination table. The NT NB scan can also be performed transvaginally. In this method, a well-lubricated ultrasound probe is inserted through the vaginal cavity to scan your uterus.

The doctor will then use the resultant photo scan to measure the nuchal translucency and check the presence of the nasal bone. This method may be slightly uncomfortable but is generally painless and completed quickly by a trained professional, without harming the baby or the mother’s health.

How to Prepare for an NT NB Scan?

You don’t need to follow any extra measures or precautions before appearing for the NT NB scan. However, you can wear comfortable and loose clothes for the scan. In addition, you can drink 2-3 glasses of water before the scan, this ensures the clear visibility of the abdomen during ultrasound.

If something else is required, your doctor will guide you based on your medical history. It’s important to remain calm while waiting for the results, as the scan is primarily a precautionary measure for most expecting mothers.

What are the Advantages of the NT NB Scan?

An NT NB scan, along with other prenatal screening tests, provides critical insights into the developing baby’s health. This includes:

  • Detecting chromosomal like Down syndrome
  • Detecting structural abnormalities like spina bifida
  • Guessing a more accurate delivery date
  • Early diagnosis of any pregnancy failure risks
  • Diagnosis of multiple foetuses (if any)

What are the Alternatives to NT NB Scan?

Generally, an NT NB scan is recommended in the first trimester to detect any congenital abnormalities. The alternative to the NT scan is non-invasive prenatal testing (NIPT), it is also known as cell-free DNA testing (cfDNA).


Due to changing lifestyles and a variety of other factors, congenital disabilities in growing babies are becoming increasingly common. If you are in the early phase of your pregnancy, you must schedule prenatal screening tests for the safety of yourself and your baby.


  • What are NT and NB scans in pregnancy?

During the first trimester, there is a fluid-filled space behind the foetus’ neck called the nuchal translucency. An NT scan is done to measure the nuchal space and estimate the risk of any chromosomal abnormalities the baby might have. The NT scan also checks if the baby has a nasal bone or not.

  • What is a normal NT NB scan?

A normal NT scan result (performed during the first trimester) will have a measurement of less than 3.5 mm. Anything wider than 3.5 mm indicates the risk of the baby having chromosomal or structural abnormalities.

  • In which week is the NT NB scan done?

The NT NB scan is performed during the first trimester (first 12 weeks of your pregnancy). The test cannot be performed after the first trimester as the baby grows larger, filling the nuchal space.

  • What happens if NT scan is not normal?

The normal NT scan measurements range from 1.6 mm to 2.4 mm. If the NT is abnormal, it suggests the fetus has chromosomal abnormalities.

  • Can NT/NB scan be done for gender identification?

No, NT/ NB scan cannot detect the gender of the baby. This scan is performed to assess the risk of chromosomal abnormalities and certain congenital conditions.

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