Nuchal translucency is no longer accurate once the crown rump length exceeds which measurement?

Nuchal translucency is no longer accurate once the crown rump length exceeds which measurement?

• A. 60 mm
• B. 84 mm
• C. 92 mm
• D. 100 mm

Answer: (B)

Nuchal translucency screening is most reliable in the early first trimester when the crown-rump length (CRL) is within a defined range, roughly up to 84 mm. This measurement is calibrated against normative data for that CRL range, and the risk estimates depend on it falling within that window. Once the CRL exceeds about 84 mm, the NT measurement becomes less accurate because the established reference standards no longer apply as reliably, and the measurement variability increases. Therefore NT is no longer a dependable marker once CRL goes beyond 84 mm. A CRL of 60 mm still falls within the validated range, while CRLs like 92 mm or 100 mm exceed the limit and NT accuracy diminishes.

Nuchal translucency screening is most reliable in the early first trimester when the crown-rump length (CRL) is within a defined range, roughly up to 84 mm. This measurement is calibrated against normative data for that CRL range, and the risk estimates depend on it falling within that window. Once the CRL exceeds about 84 mm, the NT measurement becomes less accurate because the established reference standards no longer apply as reliably, and the measurement variability increases. Therefore NT is no longer a dependable marker once CRL goes beyond 84 mm. A CRL of 60 mm still falls within the validated range, while CRLs like 92 mm or 100 mm exceed the limit and NT accuracy diminishes.