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Down's syndrome scan avoids invasive tests

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A new blood test to identify Down’s syndrome may remove the need for pregnant women to have invasive procedures to test if their baby has the condition.

The test was developed by scientists in Hong Kong, who say the it is extremely accurate. It scans the baby’s DNA to check the number of copies of chromosome 21; those with the condition have three copies instead of the usual two.

The current NHS test involves tests for protein and hormone levels and a scan to determine the space between the baby’s nape and the spine. Baby’s who have Down’s syndrome typically have more fluid gathering in the neck area compared with normally developing children.

The tests can create false alarms however. Around 5% of women are mistakenly told their baby has the syndrome when it does not.

When a baby is diagnosed with the syndrome, the pregnant mother then undergoes further, more obtrusive tests such as amniocentesis and chorionic villus sampling, which both carry a 1% risk of miscarriage.

However, the scientists in Hong Kong, writing in the British Medical Journal, insist that the need for these invasive procedure can be almost entirely removed if women were given the DNA blood test instead.

They wrote: “If we took into consideration the results of the sequencing test, trisomy 21 (Down’s syndrome) 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.”

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