In about 80% of fetuses with trisomies 21, 18 or 13 and Turner syndrome the
re is an increased collection of fluid in the neck region that can be visua
lized sonographically at 10-14 weeks gestation as increased nuchal transluc
ency thickness. The pathophysiology of this common phenotypic expression of
different chromosomal abnormalities is uncertain, but there is some eviden
ce that the underlying mechanism may be cardiac failure, possibly due to ab
normalities of the heart and great arteries, and altered composition of the
extracellular matrix of tissues, which can be also noticed in the skin. Th
e latter may be due to a gene dosage effect of the three rather than the no
rmal two copies of genes found in trisomies, causing an alteration of the e
xtracellular matrix in the skin or abnormal development of the heart and gr
eat arteries.