Morphological classification of nuchal skin in human fetuses with trisomy 21, 18, and 13 at 12 - 18 weeks and in a trisomy 16 mouse. - von Kaisenberg,C.S.; Krenn,V.; Ludwig,M.; Nicolaides,K.H.; Brand-Saberi,B. (Anat Embryol (Berl), 1998)