To describe the distribution of the fetal nuchal translucency thickness (NT) according to type of chromosomal aberration in a large unselected population.
Data on pregnancies with an NT measurement performed at gestational age 11 + 3 - 13 + 6 weeks from 2008 to 2011 were retrieved from the Danish National Fetal Medicine Database. Information on any genetic analysis for aneuploidy performed pre- or postnatally was also obtained. The abnormal results were grouped into 14 types of chromosomal anomalies. Distributions of NT measurements were summarized by aberration and compared with the normal/no karyotype group.
A total of 215 223 singleton pregnancies were included in the cohort; 10548 had a normal karyotype and 1286 had an aberration. Plots of the NT measurements showed that like trisomy 21, 18 and 13 and monosomy X, the distribution for the unbalanced translocations was shifted towards larger NTs. The distributions for the balanced translocations, the uncommon trisomies and the triploidies more closely resembled that of the normal/no karyotype population.
Fetuses with aneuploidies have NT distributions visually different from normal fetuses, with the exception of triploidies and uncommon autosomal trisomies. The distributions differ in shape according to type of chromosomal anomaly.