The 11-14 weeks scan - KH Nicolaides, NJ Sebire, RJM Snijders, AP Souka
Chapter 1
FIRST TRIMESTER DIAGNOSIS OF CHROMOSOMAL DEFECTS
In 1866, Langdon Down reported that in individuals with trisomy 21, the condition that came to bear his name, the skin appears to be too large for the body, the nose is small and the face is flat. In the last decade it has become possible to observe these features by ultrasound examination in the third month of intrauterine life. About 75% of trisomy 21 fetuses have increased nuchal translucency (NT) thickness and 70% have absent nasal bone (Figures 1 and 2).
Figure 1 Fetus with subcutaneous collection of fluid at the back of the neck. Image kindly provided by Dr Eva Pajkrt, University of Amsterdam
Figure 2 Ultrasound picture of a 12-week fetus with trisomy 21, demonstrating increased nuchal translucency thickness and absent nasal bone
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