New Delhi, Oct. 6: Scientists have developed a new test to spot Down Syndrome in a foetus through a sample of the mother’s blood — an alternative to existing invasive, and potentially-risky, procedures that use foetal tissues or amniotic fluid.

Researchers at Stanford University in the US announced today that they have used a DNA sequencing technique to successfully identify the chromosomal disorder called Down Syndrome as early as the 14th week of foetal gestation.

The non-invasive genetic test promises “minimal risk to the foetus and true genetic information”, bioengineer Stephen Quake and his colleagues said in a report that will appear today in the Proceedings of the National Academy of Sciences.

The researchers have demonstrated a prototype test that will need to be validated through large-scale studies, but it has bolstered hopes for a non-invasive method to detect congenital disorders — without extracting material from the womb.

A foetus with Down Syndrome has three copies of chromosome 21, instead of the normal two.

Doctors estimate that the incidence of Down Syndrome is about one in 1,000 foetuses, but the risk increases with the age of the mother.

“A maternal blood test to detect Down Syndrome would be very significant,” said Madhulika Kabra, an additional professor of paediatrics who runs a prenatal diagnostic clinic to screen foetuses for congenital disorders at the All India Institute of Medical Sciences, New Delhi.

“At present, definitive diagnosis of Down Syndrome is only through amniotic fluid or foetal tissue samples,” Kabra told The Telegraph.

The existing procedures have a small but non-negligible risk because of which the prenatal diagnostic procedure is primarily offered only to women considered at risk because of late age of pregnancy or other factors.

Quake’s team analy- sed free-floating DNA in maternal blood through a technique called “shotgun sequencing”. About 10 per cent of this free-floating DNA comes from the foetus.

The researchers amplified short segments of the DNA and examined the chromosomes, assuming that an extra copy of chromosome 21 in any of the samples would signal Down Syndrome in the foetus.

The cost of sequencing a sample is about $700 (Rs 33,550), the scientists said in their research report. But they expressed opti-mism that sequencing costs were likely to “drop dramatically in the near future”.