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Nuchal translucency sonography

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Nuchal translucency refers to the normal space that is visible between the spine and overlying skin at the back of the fetal neck during first‐trimester sonography (Figures 5.1 and 5.2). The larger this space, the higher the risk for trisomy 21, while the smaller the space, the lower the risk for trisomy 21. Measurement of the NT between 11 weeks and 3 days and 14 weeks and 2 days of gestation (45–84 mm) has been shown to be a useful sonographic marker for trisomy 21. Table 5.1 describes the components of a standardized NT sonographic protocol.

Nuchal translucency sonography can be technically challenging to master and it requires considerable effort to maintain quality over time. Given the importance of maintaining such accuracy, sonographers and physicians who provide this form of screening should be credentialed and enrolled in an ongoing quality assurance program. Examples of such QA programs include the Nuchal Translucency Quality Review (NTQR) managed by the Perinatal Quality Foundation in the US (www.ntqr.org) and the Fetal Medicine Foundation in Europe (www.fetalmedicine.org).


Figure 5.1 Nuchal translucency (NT) ultrasound measurement at 13 weeks’ gestation in a chromosomally normal fetus, measuring 1.5 mm. Various features of good NT ultrasound technique are evident in this image: adequate image magnification, midsagittal plane, neutral neck position, inner to inner caliper placement perpendicular to the fetal body axis, and separate visualization of the overlying fetal skin and amnion.

Source: Mary E. Norton, MD.


Figure 5.2 Increased nuchal translucency measurement at 13 weeks’ gestation in a fetus with Down syndrome.

Source: Mary E. Norton, MD.

Table 5.1 Nuchal translucency (NT) measurement criteria of the Nuchal Translucency Quality Review (NTQR) Program

1 Fetal head, neck, and upper thorax should fill the majority of the image (>50%)
2 Image should be optimized so the NT lines are thin and clear
3 Fetus should be examined in a midsagittal plane
4 Fetal neck should be in a neutral position
5 Fetus should be observed away from the amnion
6 The “+” calipers should be used
7 Calipers should be placed on the echogenic inner borders of the nuchal membranes with none of the horizontal crossbars protruding into the translucent NT space
8 Calipers should be placed perpendicular to the long axis of the fetal body
9 At least three nuchal translucency measurements should be obtained and the maximum acceptable measurement should be used
10 The ALARA (as low as reasonably achievable) criteria should be followed and the thermal index for bone (TIB) set with an output standardized display of ≤0.7

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