[Fetal nuchal translucency]

Abstract

In addition to its role in the assessment of risk for trisomy 21, increased nuchal translucency (NT) thickness can also identify a high proportion of other chromosomal defects and is associated with major abnormalities of the heart and great arteries, and a wide range of genetic syndromes. In the first trimester, the term translucency is used to describe the accumulation of fluid behind the fetal neck, irrespective of whether it is septated or not and whether it is confined to the neck or envelopes the whole fetus. During the second trimester, the translucency usually resolves and, in a few cases, it evolves into either nuchal edema or cystic hygromas with or without generalized hydrops. Increased NT is associated with trisomy 21, Turner syndrome and other chromosomal defects as well as many fetal malformations and genetic syndromes. The incidence of these abnormalities is related to the thickness, rather than the appearance, of NT The ability to achieve a reliable measurement of NT is dependent on appropriate training and adherence to a standard technique in order to achieve uniformity of results among different operators. Furthermore, the success of a screening program necessitates the presence of a system for regular audit of results and continuous assessment of the quality of images.