Is a nuchal translucency (NT) measurement of 0.3mm considered normal in a pregnancy?

A Nuchal Translucency Measurement of 0.3mm is Abnormally Low and Likely Represents a Measurement Error

This measurement of 0.3mm is far below the expected range for any gestational age between 11-14 weeks and should prompt immediate remeasurement using proper technique. Normal NT values at this gestational window typically range from approximately 1.0-2.5mm depending on crown-rump length, making 0.3mm physiologically implausible 1, 2.

Understanding Normal NT Values

• The American College of Radiology defines increased NT as ≥3mm or above the 99th percentile for crown-rump length, but normal NT measurements are substantially higher than 0.3mm at any point in the 11-14 week window 1, 2.

• NT measurement is crown-rump length dependent and must be obtained between 11+0 to 14+0 weeks of gestation, as the measurement loses predictive value outside this narrow window 2, 3.

• The hypoechoic space between the overlying skin and underlying soft tissues of the posterior cervical spine should be clearly visible and measurable, typically ranging from 1-2.5mm in normal fetuses 1, 4.

Why 0.3mm is Problematic

• A measurement this low suggests technical error in image acquisition or caliper placement rather than a true anatomic finding 4.

• The Nuchal Translucency Quality Review Program has established nine specific criteria for accurate NT measurement, and failure to meet these standards results in significant inter- and intra-observer variability 2, 4.

• Quality assurance and ongoing training are essential because there is considerable measurement variability, and a 0.3mm reading falls well outside the physiologic range 2.

Immediate Next Steps

• Request remeasurement by a certified sonographer or maternal-fetal medicine specialist using standardized Fetal Medicine Foundation techniques 2, 4.

• Ensure the measurement is obtained with:

  • Proper fetal positioning (neutral neck position, not flexed or extended) 4
  • Adequate magnification (fetus occupying 75% of the image) 4
  • Correct caliper placement (on the inner borders of the translucent space) 4
  • Mid-sagittal plane visualization 4

• Verify crown-rump length to confirm gestational age is within the 11-14 week window 1, 2.

Clinical Context

• Even if remeasurement yields a normal value (1.0-2.5mm), this does not eliminate all risk—NT screening alone detects only approximately 70% of trisomy 21 cases, meaning 30% of Down syndrome fetuses will have normal NT measurements 2, 5.

• First trimester combined screening (NT + PAPP-A + free β-hCG) should still be offered, as it detects approximately 90% of affected pregnancies with a 5% false-positive rate 1, 2.

• A standard second trimester anatomic survey at 18-22 weeks remains mandatory regardless of first trimester NT results, as only about 50% of major fetal anomalies can be detected prior to 14 weeks 2, 5.

Common Pitfall to Avoid

• Do not interpret an abnormally low measurement as "reassuring"—it represents technical inadequacy requiring correction 4. The measurement should be repeated until a technically adequate image meeting all quality criteria is obtained 2, 4.