New blood test for Down's syndrome
A blood test to check for Down's syndrome could almost eliminate the need for invasive procedures, new research has suggested.
The highly accurate test looks at the genetic material DNA to predict whether a woman is carrying a baby with the syndrome.
People with Down's have three copies of chromosome number 21 rather than the usual two.
Current testing on the NHS combines a blood test to check levels of some proteins and hormones with a scan to measure the space between the spine and the nape of the baby's neck. The "false positive" rate of these tests is about 5%, meaning 5% will be told they are carrying a Down's baby when they are not.
All of these pregnant women are then offered the option of further, invasive tests including amniocentesis or chorionic villus sampling, which have about a 1% risk of miscarriage.
If these women were given the DNA blood test instead, almost all invasive procedures could be avoided, according to experts from Hong Kong, writing in the British Medical Journal (BMJ).
They wrote: "If we took into consideration the results of the sequencing test, trisomy 21 (Down's) could be ruled out in 98% of those pregnancies.
"This would leave just 0.1% of all pregnant women needing referrals for amniocentesis or chorionic villus sampling."
The experts used the most up-to-date DNA technology to test blood samples from 753 high-risk pregnant women in Hong Kong, the UK and the Netherlands. The results showed that the test was highly accurate in detecting Down's and did not miss any cases.
The number of babies diagnosed with Down's syndrome has risen sharply in the past 20 or more years - largely due to women delaying motherhood, other research has shown.