Ultrasonographic Soft Markers of Aneuploidy in Second Trimester: Are We Lost?

Sameer Raniga, MD, DNB; P.D. Desai, MD; Hetal Parikh, MD

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In This Article

Nuchal Fold Thickening

Nuchal edema in the second trimester between 15 and 23 weeks is known as the nuchal fold. Nuchal thickening was the first of the nonstructural markers identified and remains the single most predictive sonographic marker.[12] The measurement is made in the transverse plane of the fetal head slightly off the biparietal diameter, which includes the cerebellum, occipital bone, and cavum septum pellucidum (Figure 1). The nuchal fold is measured with placement of calipers from the outer edge of occipital bone to the outer edge of the skin.[21,22] Initial studies suggested a cutoff of 6 mm,[10,23,24,25] although subsequent studies with ROC curve analysis suggested that 5 mm is a better single cutoff before 20 weeks.[26,27] Even more recent studies suggest that gestational age-specific criteria should be used, because nuchal thickness normally increases with gestational age.[28,29,30] Multiples of the median and associated likelihood ratios (LRs)1 can then be calculated for the entire range of nuchal thickness measurements.[28,29]

Figure 1.

Axial image of the fetal head shows thickening of nuchal fold. Nuchal fold is measured during the second trimester on an axial image slightly off the biparietal diameter plane. The cerebellum, cisterna magna, and occipital bone should be seen. Soft tissue is measured from the outer echogenic line of occipital bone to the outer echogenic skin line.

Source: Pilu G, Nicolaides K, Ximenes R, Jeanty P. Diagnosis of fetal abnormalities. The 18-23 week scan. Diploma in Fetal Medicine. ISUOG Educational Committee. Copyright 2002 © by the authors and ISUOG. Reprinted with permission.

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