Increased nuchal translucency in trisomy 21 fetuses: relationship to narrowing of the aortic isthmus.

Pathological examination of the great vessels was performed in 34 trisomy 21 fetuses after surgical termination of pregnancy at 11-16 weeks of gestation. In each case, the external diameters of eight segments of the great vessels were measured. The aortic valve and the ascending aorta were wider than in normal fetuses, whilst the aortic isthmus was narrower. The degree of narrowing of the isthmus was significantly greater in fetuses with high nuchal translucency thickness and it is possible that there is a causal association between the two.