The combined ultrasound and blood test will be done up to two months earlier than at present and is 90% accurate compared with 65% for the current procedure.

The new test – called nuchal translucency – will mean fewer women will need to undergo an invasive procedure to confirm Down's, which carries a risk of causing a miscarriage.

Early diagnosis of Down's will allow mothers longer to prepare for birth and give doctors more opportunities to monitor the baby. It will also allow women extra time to decide whether or not to have an abortion.

Down's is caused by an extra copy of a chromosome inside each of the body's cells, causing learning difficulties, a range of physical health problems, and reduced life expectancy.

The current blood test generates a significant number of "false positive" results. Confirmation of the condition is by a procedure called amniocentesis which involves inserting a needle into the womb and extracting amniotic fluid. The test carries a 1% risk of causing a miscarriage, meaning some women decide not to be tested.

Last night, Health Secretary Nicola Sturgeon told Scotland on Sunday the new test would be introduced throughout the country within three years, as part of a £11.5m programme to improve screening in pregnancy.

Sturgeon said: "We intend to offer a combined ultrasound and biochemical screening test during the first trimester for a majority of women which will help increase the detection rate for Down's Syndrome and reduce the number of false positive results.

"We will also ensure that an enhanced test is offered later in pregnancies when, for whatever reason, a mother has presented later."

The nuchal translucency test has been on offer to women in England for a number of years but health boards in Scotland have failed to offer it routinely because of a lack of trained staff.

It is currently available only to a limited number of women in Scotland, including patients at Glasgow's Queen Mother's Hospital. NHS Borders offers it to women over the age of 38 while NHS Lothian plans to offer it routinely to all women from September.

However, Sturgeon said that all areas will offer the procedure by March 2011. It will be carried out within the first three months of pregnancy, compared with up to 18 weeks at present.

Last night, Scottish health campaigners welcomed the move but warned against pressurising women to have abortions.

Around 90% of women who find out they are carrying a child with Down's Syndrome make the decision to terminate the pregnancy.

Pandora Summerfield, director of the charity Down's Syndrome Scotland, said: "Women should be able to make informed choices. However, when given the results of a test like this which shows they might have a baby with Down's, they should be given the opportunity to find out what that means rather than automatically thinking the worst.

"The world has moved on significantly and this diagnosis is not the bleak scenario that it used to be. We do not believe that a diagnosis of Down's Syndrome should be an automatic reason for a termination."

Gillian Smith, director of the Royal College of Midwives in Scotland, said: "We are delighted that this is now going to be offered as it will identify Down's Syndrome better than existing screening. It is up to women to decide whether to take it or not because once the decision is taken to have the test it does set women on a path of having to take more decisions if the results show a high risk."

A spokeswoman for the pro-life charity Society for the Protection of the Unborn Child said: "The fact is by constantly suggesting pregnant women should be tested in this way we create a fear of disabilities such as Down's."

One mother of a child with Down's Syndrome said yesterday that she did not think the programme was the right way forward for the NHS

Lynn Murray's eight-year-old daughter Rachel attends mainstream school and enjoys ballet and swimming. Murray had chosen not to be tested during pregnancy and though she was "devastated" when Rachel was born she says her daughter is now leading a happy life.

She added: "Rachel has a lovely personality, she is very outgoing and everyone loves her. I do not think this test is going to benefit people with Down's."