Korean J Obstet Gynecol.  2010 Jan;53(1):1-14. 10.5468/kjog.2010.53.1.1.

Clinical implications of nuchal translucency

• Choi SJ

• KMID: 2077954
• DOI: http://doi.org/10.5468/kjog.2010.53.1.1

Abstract

Fetal nuchal translucency (NT) is an echolucent space between the dorsal edge of soft tissue of the fetal neck and the linear echo of the skin observed in a midsagittal image measured at 11 to 13(+6) weeks of gestation. Increased NT (>95 percentile) is highly associated with fetal aneuploidy and congenital structural anomalies including congenital heart defects. In combination with maternal serum PAPP-A and free beta-hCG, increased NT has been demonstrated to provide efficient Down syndrome risk assessment, with a detection rate of 80-87% (5% false-positive rate), and it also allows earlier diagnosis of fetal aneuploidy. Even in the absence of aneuploidy, increased NT is still associated with an increase in adverse perinatal outcome including abortion, fetal death and a variety of fetal malformations. This paper will review the mechanism of increased NT, correct measurement of NT, and recent evidences for interpretation and management for the fetuses with increased NT.

Keyword

Nuchal translucency; fetal aneuploidy; congenital anomaly

MeSH Terms

Aneuploidy
Down Syndrome
Fetal Death
Fetus
Heart Defects, Congenital
Neck
Nuchal Translucency Measurement
Pregnancy
Pregnancy-Associated Plasma Protein-A
Risk Assessment
Skin
Pregnancy-Associated Plasma Protein-A

Figure

• 

  Fig. 1 (A) Fetal nuchal translucency (NT) is an echolucent space (arrow) between the dorsal edge of soft tissue of the fetal neck and the linear echo of the skin observed in a midsagittal image. (B) Gross image of the fetus with an abnormally increased NT (open arrow)2

• 

  Fig. 2 Examples of nuchal translucency (NT) measurements. (A) Improper midsagittal plane and inadequate magnification. (B) Proper midsagittal orientation, but inadequate magnification. However, the amnion is clearly seen distinctly from the NT. (C) Proper midsagittal orientation and adequate magnification. The fetus (head, neck, chest) fills more than 75% of the image. However, there is no echolucent space between the fetal chin and chest. NT may be underestimated when measured in a fetus with a flexed head. Contrarily, NT may be overestimated when measured in a fetus with an overextended head. (D) Fetal neck is in a neutral position with an echolucent space (*) between the fetal chin and chest. But, dorsal fetal skin is not distinguished from the amnion. (E) Improper midsagittal plane. Ultrasound beam is not perpendicular to the long axis of the NT, therefore proper caliper placement may not be feasible. (F) Proper midsagittal orientation, adequate magnification, and neutral fetal neck.

• 

  Fig. 3 (A) Proper placement of the calipers for nuchal translucency (NT) measurement. The calipers should be placed at the innermost edge of the echogenic lines, so that the crossbars coincide with the inner border of the echogenic lines. (B-F) Improper placements of the calipers. (B) The calipers are placed at the outermost edge of the echogenic lines. (C) The calipers are placed in the center of the echogenic lines. (D) The calipers are not aligned perpendicular to the long axis of the NT. (E) The crossbars of the calipers are visible within the sonolucent space. (F) The calipers are relative well aligned perpendicular to the long axis of the nuchal translucency, and caliper placement is proper, however, NT is not measured in the maximal thickness.

• 

  Fig. 4 (A) Abnormally increased nuchal translucency (NT) in a fetus at 13 weeks of gestation. (B) A cystic hygroma in a fetus at 13 week of gestation. Septations and trabeculae are visible within the cystic hygroma. (C) Follow up ultrasound image of the fetus in the figure (B) at 21 weeks of gestation. Fetal karyotype was normal and no additional abnormality was found in the targeted ultrasound including fetal echo. However, persistent cystic hygroma (arrow) was still visible. (D) Another case of huge cystic hygroma diagnosed at 12 weeks of gestation. This fetus ultimately progressed to general fetal hydrops.2

• 

  Fig. 5 Abnormally increased nuchal translucency (NT) in a fetus at 13 weeks of gestation. (A) Nasal bone is invisible under the nasal skin shadow (arrow). (B) 3D image of the same fetus. (C) Reversed A-wave of ductus venous Doppler flow. (D) Complex fetal heart defect was diagnosed by the fetal echo (functionally single ventricle with a large VSD and pulmonary atresia).2

• 

  Fig. 6 Twin pregnancy at 12 weeks of gestation. (A) One twin (1) had a cystic hygroma extending along the entire length of the fetus and in which septations are clearly visible. However, the co-twin was normal. (B) 3D image the twin pregnancy.2

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  Fig. 7 Algorithm for management of fetuses with increased nuchal translucency.

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