New blood test for Down's syndrome

A new blood test can reliably show whether an unborn baby has Down's syndrome, claim researchers.

The non-invasive tests at the 10-week stage on 1,005 pregnancies proved to be more sensitive at detecting the condition.

The study revealed that they were more sensitive at detection and there were fewer "false positive" results than the combined tests normally performed between the 11-13 week stage.

The study concerned is the first to examine the feasibility of screening for chromosomal disorders called trisomies, making use of foetal cell free DNA (cfDNA) from the blood of a pregnant woman.

The cfDNA test returned false positive rates of 0.1% compared with 3.4% for the combined tests. It was found if cfDNA testing was performed after a combined test at 11 to 13 weeks, a 98% detection rate of Down's syndrome was possible, meaning less than 0.5% of cases needed invasive testing for confirmation.

The study, performed at the Harris Birthright Centre at King's College London, showed the big reduction in false positive rates to be the main plus of cfDNA testing, in comparison with the combined test, said the authors.

Another big advantage was the reporting of results as very high or very low risk, easing the decision of parents to be for or against invasive testing.

The study was published in the Ultrasound in Obstetrics & Gynecology  journal.
At present, Down's syndrome is tested for between the 11th and 13th weeks of pregnancy with an ultrasound screen and hormonal analysis of the woman's blood. The only definitive test involves chorionic villus sampling and amniocentesis, which carries a risk of miscarriage.

Copyright Press Association 2013


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