Is NT of 0.6mm Normal?
Yes, a nuchal translucency measurement of 0.6mm is completely normal and reassuring—this measurement is well below the threshold of concern (≥3mm) and falls within the expected range for first trimester fetuses. 1
Understanding Normal NT Values
- NT naturally increases with crown-rump length during the 11-14 week window, so gestational age must be considered when interpreting measurements. 1, 2
- An increased NT is defined as ≥3mm or above the 99th percentile for the crown-rump length—your measurement of 0.6mm is far below this threshold. 1, 2
- The American College of Radiology defines NT as the hypoechoic space between the overlying skin and underlying soft tissues of the posterior cervical spine, and below the defined threshold of 3mm, this translucent space is considered a normal ultrasound finding. 1
What This Normal Measurement Means
- A normal NT significantly reduces (but does not eliminate) the risk of chromosomal abnormalities, as NT alone detects approximately 70% of trisomy 21 cases, meaning 30% of Down syndrome fetuses will have normal NT measurements. 3, 4
- Less than 25% of major heart defects are detected using NT screening at the 99th percentile in chromosomally normal fetuses, confirming that most congenital heart disease cases have normal NT thickness. 3, 4
- Only about 50% of major fetal anomalies can be detected prior to 14 weeks with a false-positive rate of 3-4% at this early gestational age. 3, 4
Critical Follow-Up Requirements
Despite your reassuring NT measurement, you must still receive:
- Standard second trimester anatomic fetal survey at 18-22 weeks—NT screening should never replace this comprehensive evaluation regardless of how normal the first trimester results appear. 3, 4
- The sensitivity of ultrasound at 11-14 weeks for detecting congenital anomalies is only about 50% compared to 75% at 18-22 weeks, making the second trimester scan essential. 3, 2
Important Clinical Caveats
- Normal NT does not exclude chromosomal abnormalities or structural defects—it simply reduces the probability but cannot rule them out. 3, 4
- If you are having first trimester combined screening (NT + PAPP-A + free β-hCG), this combination detects approximately 90% of affected pregnancies with a 5% false-positive rate, which is more accurate than NT measurement alone. 1, 3
- If you had negative cell-free fetal DNA screening (like Panorama), the second trimester anatomic survey is still required even with your normal NT, as structural defects and certain genetic conditions can be missed by both tests. 4