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Screening and testing during pregnancy

Around one in every thousand babies will have Down’s syndrome. It is present from the moment of conception and is caused by an extra chromosome being present in each cell. This extra chromosome causes there to be more protein in the cells of the baby’s body and this protein affects the way that the baby develops in the womb.

When a pregnant woman’s blood is taken, an increased level of protein in the blood sample could mean that the baby has Down’s syndrome. A risk factor is calculated using the measure of protein and the mother’s age. If the risk of the baby having Down’s syndrome is 1 in 251 or higher, no further action will be taken. However, if the risk is 1 in 250 or less, further screening is offered.

A detailed scan may be offered where the radiographer will look for signs that the baby has Down’s syndrome. However only invasive testing such as amniocentesis or chorionic villus sampling (CVS) can identify for definite that the baby has Down’s syndrome. Both of these tests carry a small risk for the pregnancy.


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