Objective: To investigate the dynamic trend of the nuchal translucency thickness between fetuses with normal and abnormal karyotype.
Design: Prospective observational study.
Setting: Ospedale Microcitemico, Cagliari, Italy.
Population: A cohort of 305 first trimester fetuses.
Methods: Fetuses with a nuchal translucency greater than or equal to the 95th centile were invited for a second nuchal translucency measurement. The finding of an 'increased or unchanged' or 'diminished' thickness was compared in fetuses with normal and abnormal karyotype.
Main outcome measures: Nuchal translucency and karyotype. Median maternal age was 35 years (min 17, max 44) and median crown-rump length at first visit was 50 mm (min 38, max 80). A second nuchal translucency measurement was carried out in 292 fetuses, resulting in increased or unchanged values in 95 cases and decreased nuchal translucency in 197 cases. Two hundred and twenty-six (77.4%) fetuses had normal karyotype and 66 (22.6%) had abnormal karyotype (44 trisomies 21, 10 trisomies 18, 5 trisomies 13, 4 cases of 45 X0, 1 case of 47,XXY, 1 case of 47,XXX and 1 translocation). In the 66 chromosomally abnormal fetuses, the second nuchal translucency measurement was enlarged or unchanged in 37 (56%), and diminished in 29 (44%), while in the 226 normal fetuses the second nuchal translucency measurement was enlarged or unchanged in 58 cases (25%) and diminished in 168 (75%) (relative risk 2.6, 95% confidence interval 1.7-4.0).
Conclusion: In fetuses with abnormal karyotype, the second nuchal translucency measurement tends to be increased or unchanged, while in normal cases the size of nuchal translucency is generally reduced.