The test, which analyses a baby's DNA from a mother's blood, is available in the United States, and some Australian mothers are opting to spend $1000 to $1200 to send their blood samples overseas to access it.

The DNA is screened for chromosomal abnormalities that may result in intellectual or physical problems in a newborn. The test, called cfDNA, can more reliably detect whether an unborn baby has Down syndrome during the first trimester and does not carry a risk of miscarriage, unlike chorionic villus sampling and amniocentesis, which are the two tests used by doctors across the nation.

Chorionic villus sampling, undertaken at 12 weeks, and amniocentesis, at 16 weeks, are considered invasive tests because a large needle is inserted through the uterus wall to extract a DNA sample.

Associate professor of obstetrics and gynaecology at the Australian National University Steve Robson said the new blood test should be made available to all women who are shown to have a high probability of carrying a Down syndrome child after a nuchal translucency test (the combined ultrasound and blood tests usually carried out between the 11th and 13th weeks of pregnancy).

According to a study by the Harris Birthright Centre at King's College London, the combined ultrasound and blood tests return false positive results in 3.5 per cent of cases, while the cfDNA test returned false positive rates of 0.1 per cent. The study also found that when carried out after combined testing, 98 per cent of cases of Down syndrome could be detected and invasive testing was only needed for confirmation in 0.5 per cent of cases.

Since February Dr Robson has had about 20 patients send their blood to the US for testing.

"From six or seven weeks of pregnancy about 5 or 6 per cent of all free DNA fragments in a woman's blood come from the baby.

''Having a needle put into the pregnancy to analyse the same result carries a risk of miscarriage. As a general rule the risk of having amniocentesis to a healthy baby is probably one chance in 150. It may sound like a small chance, but over the years I've had a couple of miscarriages [as a result of amniocentesis] and it's an absolutely devastating situation.''

He said the cfDNA test should not be used instead of the combined tests, but instead of amniocentesis when the results of the ultrasound and initial blood tests were not reassuring.

"The NT test also provides information about the heart and development, which you don't get out of DNA testing. It really only gives you information about Down syndrome and some other chromosomal abnormalities.''

Dr Robson also warned the current situation created a division between those who could afford better diagnostic tests and those who could not.

"It would be a terrible situation where only the wealthy could have this test,'' he said.

A spokesman from the Department of Health said the test could be subsidised under the Medicare Benefits Schedule, but no applications to bring the test to Australia had been received. Dr Robson said subsidising the test in Australia would give women peace of mind.