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The DNA screening test

The DNA screening test is the most effective method of screening for Down's syndrome (T21), trisomy 18 (T18) and trisomy 13 (T13).

This page explains:

What does the DNA screening test involve?

The DNA screening test is performed from 10 weeks of pregnancy.

The test involves:

Taking a sample of your blood to measure cell free DNA that is circulating in the mother’s blood during pregnancy.  This DNA comes from both the mother and the baby.

In pregnancies with T21, T18 or T13 there will be a little bit more DNA from chromosomes 21, 18 or 13 respectively.

Can any other abnormalities be identified?

No.  The test currently identifies pregnancies with T21, T18 or T13.  It cannot detect other chromosomal abnormalities.

What is defined as a screen-positive result?

If the risk of having a term pregnancy affected with T21, T18 or T13 is 1 in 150 or higher you will be offered an amniocentesis

The DNA screening test is not a replacement for diagnostic tests such as amniocentesis or chorionic villus sampling. 

If you have a screen-positive result following the DNA screening test it is recommended you have an amniocentesis to confirm whether the pregnancy is affected with T21, T18 or T13 or not.

Performance of the DNA screening test using a 1 in 150 at term cut-off

Detection Rate (DR)

About 99% of women with pregnancies affected with T21, T18 or T13 will receive a screen-positive result. (The remaining 1% of women with pregnancies affected with Down's syndrome will receive a screen-negative result.)

False Positive Rate (FPR)

About 0.1% of women (1 in every 1,000 tests performed) whose pregnancies are not affected with Down's syndrome will receive a screen positive result. (99.9% of women whose pregnancies are not affected with Down's syndrome will receive a screen-negative result).

Arranging a DNA screening test

The DNA screening test is performed by the Antenatal Screening Service at the Wolfson Institute.
For further information please contact us on +44 (0)20 7882 6293.

Cost

The cost of the DNA screening test is £300.

Information leaflets

The Antenatal Screening Service has produced an information leaflet for the DNA screening test.

Download the leaflets in PDF format:

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