In pregnancy, NB stands for nasal bone.
Understanding Nasal Bone in Prenatal Scans
The presence or absence of the nasal bone (NB) is a crucial marker assessed during the first-trimester screening, particularly the Nuchal Translucency (NT) scan, usually performed between 11 and 14 weeks of gestation. This scan combines the measurement of the fluid-filled space at the back of the baby's neck (nuchal fold thickness) with the assessment of the nasal bone.
Why is the Nasal Bone Important?
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Screening for Chromosomal Abnormalities: According to the reference, an absence or hypoplasia (underdevelopment) of the nasal bone, alongside an increased nuchal fold thickness, can be a soft marker for chromosomal abnormalities, such as Down syndrome.
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Not a Diagnostic Test: It is essential to understand that an absent nasal bone is not a definite diagnosis of Down syndrome or any other condition. It's merely an indicator that warrants further investigation with more specific tests like Chorionic Villus Sampling (CVS) or amniocentesis.
What Happens During an NT Scan?
During an NT scan, an ultrasound technician will assess:
- Nuchal Fold Thickness: They measure the fluid-filled space at the back of the baby's neck. An overly thick nuchal fold can also be a marker for chromosomal abnormalities.
- Nasal Bone Visualization: They look to see if the nasal bone is visible and assess its size.
Interpreting Results
The results from an NT scan, including the presence or absence of the nasal bone, are combined with the mother's age and other factors to calculate the risk of chromosomal abnormalities. If the results indicate an increased risk, further tests might be recommended.
In Summary
| Feature | Description | Significance |
|---|---|---|
| NB | Nasal Bone | Its presence is assessed during the first-trimester NT scan. |
| NT Scan | Nuchal Translucency scan performed between 11 and 14 weeks | Examines both nuchal fold thickness and nasal bone visibility. |
| Significance | Absence or underdevelopment, especially with increased nuchal fold, can indicate higher risk for chromosomal abnormalities, such as Down syndrome | Requires further diagnostic testing to confirm or rule out chromosomal conditions, and does not provide a definitive diagnosis. |
