NT NB Scan

The NT NB Scan is a specialised first-trimester ultrasound that combines two important assessments of your baby’s early development:

Nuchal Translucency (NT)

• The NT scan full form is Nuchal Translucency Scan.
• It measures the fluid-filled space at the back of the baby’s neck, known as the nuchal translucency.
• This measurement is used as one of the markers in first-trimester screening.

Nasal Bone (NB)

• NB stands for Nasal Bone.
• During the scan, the sonographer checks whether the baby’s nasal bone is visible and developing appropriately for the stage of pregnancy.
• The nasal bone assessment complements the NT measurement and forms an important part of the screening process.

Together, the NT NB scan measurements help estimate the likelihood of chromosomal abnormalities and support early pregnancy assessment.

What is the Purpose of the NT NB Scan?

The primary purpose of the NT NB Scan is to check whether the pregnancy is at a higher risk of certain chromosomal conditions. It is a screening test and not a diagnostic test.

Screening for Down Syndrome

One of the more common reasons for an NT NB Scan is to evaluate a baby for the risk of having Down syndrome (Trisomy 21) in the first trimester. Babies with Down syndrome are found to have increased nuchal translucency thickness or an underdeveloped/absent nasal bone. When combined with maternal age and blood test results, the scan helps estimate the baby’s risk.

Screening for Trisomy 18

The NT NB scan also helps identify the risk of Trisomy 18 which is also called Edwards syndrome. It is a rare genetic condition associated with significant developmental abnormalities. Increased NT measurements in certain cases may indicate a higher chance of this condition.

Screening for Trisomy 13

Trisomy 13 is another condition which is assessed through NT screening. This is also called Patau syndrome. Babies affected by this condition often have severe developmental abnormalities that may be detected through early screening and follow-up investigations.

Early Assessment of Fetal Development

NT NB scan is an important part of routine first-trimester pregnancy care. Besides screening for chromosomal abnormalities, the scan allows doctors to

• Confirm fetal viability
• Assess growth and development
• Check gestational age
• Evaluate early anatomical structures
• Confirm the presence of the nasal bone

Supporting Further Diagnostic Decisions

If the NT NB scan report suggests an increased risk, your doctor may recommend additional testing such as

• Non-Invasive Prenatal Testing (NIPT)
• Chorionic Villus Sampling (CVS)
• Amniocentesis
• Detailed anomaly scans

These tests can provide more definitive information when needed.

When is the Best Time for an NT/NB Scan?

One of the common questions that most expecting parents have is “Which week is best for an NT NB scan?” According to the doctor’s advice, NT NB Scan should be done anytime between 11 weeks and 14 weeks pregnancy as:

• The size of the fetus at this point is ideal for precise measuring.
• At this age, the translucency of the nuchal region can be measured accurately.
• Reliable time for nasal bone assessment.

Therefore, the dates for NT NB Scan are generally prescribed such that you are never too early nor too late to ensure accurate results.

What is the Procedure for an NT/NB Scan?

The NT NB scan is a simple procedure which is performed by a trained medical professional and does not involve injections or anaesthesia.

How is the NT NB Scan Done Step-by-Step?

The process involves the following steps:

Step 1: Prepare for the scan: You might be asked to drink water beforehand, especially in early pregnancy, as a full bladder improves image quality.

Step 2: Ultrasound Scanning: The medical professional will apply some gel on your abdomen and move an ultrasound probe over it to capture pictures of the fetus.

Step 3: Measurement of Nuchal Transparency: The fluid-filled space behind the baby’s neck is carefully measured. Precision is important because even a small difference in measurement can impact risk assessment.

Step 4: Evaluation Of The Nasal Bone: The technician then ascertains if the baby has a visible nasal bone.

Step 5: Measurements Documentation: The results are subsequently recorded and placed in the NT NB scan report. The entire process would typically take approximately 20 to 40 minutes depending on the baby’s positioning.

Is the NT Scan Painful for the Mother or Baby?

No, the NT scan is not painful. It utilises ultrasound waves which is similar to other standard pregnancy ultrasounds. The pressure felt as the scanning probe is pressed onto the stomach might cause mild discomfort but it would not hurt the mother and baby. NT NB scan is a safe and quick procedure when done by trained professionals.

What is the Normal Range of NT/NB Scan?

The exact normal value varies according to the baby’s gestational age and crown-rump length. In general,

• NT measurement below 3.0 mm is often considered within the expected range
• Measurements above the expected range may require further evaluation

For the nasal bone,

• The nasal bone should usually be visible during the scan
• Absence or underdevelopment may increase the calculated risk for certain chromosomal conditions

It is important to remember that an abnormal screening result does not necessarily mean the baby has a chromosomal condition. It simply indicates that additional assessment may be beneficial.