Nuchal Translucency Scan

Down’s Syndrome is the most common cause of learning disability. It is a chromosomal abnormality caused by the presence of an extra chromosome 21. The chance of having a baby with Down’s Syndrome increases as the mother gets older but there is a risk for women of all ages. The Combined Test is a screening test that measures various ultrasound and biochemical (substances in the mothers blood) markers to give an individualised risk of a pregnancy being affected with Down’s Syndrome.

The ultrasound markers that are utilised for the test are measurement of the nuchal translucency, presence or absence of the nasal bone and tricuspid regurgitation, assessment of flow in the ductus venosus and detailed examination of the babies anatomy. Maternal blood is also taken to measure levels of Beta Human Chorionic Gonadotrophin (the pregnancy hormone) and Pregnancy Associated Plasma Protein A (a protein produced by the developing placenta). The findings from the various assessments are then combined to give an individualised risk of the pregnancy being affected by Down’s Syndrome. The Combined Test can be performed between 11 weeks and 13 weeks and 6 days of pregnancy.

A risk of 1 in 300 or greater is considered to be “screen positive”. Women with a screen positive result will be offered counselling and a definitive diagnostic test i.e. CVS or amniocentesis.