NT NB SCAN

An NB (nasal bone) and NT (nuchal translucency) scan are first‑trimester ultrasound assessments, usually at 11–14 weeks. NT measures fluid at the back of the fetus’s neck; increased thickness may signal chromosomal or cardiac issues. NB checks for presence or size of the fetal nasal bone; absence or hypoplasia raises risk. Together with maternal blood tests they estimate Down syndrome and other anomaly risk.

The NT/NB scan (11–13+6 weeks) screens for chromosomal abnormalities by measuring nuchal translucency and checking the nasal bone. It is not a reliable test to determine fetal sex. Sonographers may sometimes guess early, but accuracy varies. For dependable results, wait for the 18–20 week anatomy scan or use noninvasive prenatal testing (cell‑free fetal DNA) or diagnostic testing.

Normal NT/NB values are assessed at 11+0–13+6 weeks. Nuchal translucency (NT) is generally considered normal when below about 3.5 mm (or under the gestation-specific 95th centile). The nasal bone (NB) is normally present and measurable at this stage; an absent or hypoplastic nasal bone is considered abnormal. Results are combined with maternal age and serum markers to estimate chromosomal risk.

Costs vary widely by country and provider. In public systems it’s often free (e.g., NHS). Private clinic fees typically run about £100–£300 in the UK, $200–$600 in the US, and roughly ₹700–₹3,000 in India. Some centres include the NT‑NB as part of combined first‑trimester screening or insurance‑covered antenatal packages—check local providers for exact pricing.

At 12 weeks’ gestation the fetal nasal bone is usually visible and typically measures about 2.0–3.0 mm (values may reach ~3.5 mm depending on crown–rump length). Absence or marked shortening of the nasal bone at this stage is a soft marker for Down syndrome and generally prompts further assessment such as detailed ultrasound, combined first‑trimester screening, or diagnostic testing.

No. NT and nasal bone scans are screening tools that identify increased risk for common chromosomal conditions (eg, Down syndrome) and some structural markers, but they do not detect all abnormalities. They can give false positives or negatives. Abnormal or high‑risk results typically prompt further testing (cell‑free DNA, detailed anomaly scan, or diagnostic CVS/amniocentesis) for definitive diagnosis.