This ultrasound assessment is offered in order to assess the nuchal translucency which is a useful screening test for estimating the risk of chromosomal abnormalities including Down’s syndrome. This is the measurement of the fluid under the skin at the back of the neck for which the higher the measurement, the higher the risk of chromosomal abnormality. The accuracy of the possibility of chromosomal abnormality is improved even more if this test is combined with the results of some biochemical markers in the maternal blood ( PAPP-A, b-HCG). The presence of the nasal bone will also reduce the possibility of chromosomal abnormality.
The result of the nuchal translucency, the biochemical markers, the presence or not of the nasal bone and the maternal age are assessed together by computer software. By bringing together the three results, it offers with greater accuracy the possibility of estimating the risk of chromosomal abnormality. If the risk for chromosomal abnormality is significant, then amniocentesis or chorionic villus sample is offered. At this stage of the pregnancy the fetus has been completely formed and therefore it is possible to exclude a good number of serious anatomical problems. This task will be continued at the ultrasound assessment of fetal anatomy that will take place later at around 20 weeks gestation.