Scientists have identifed a technique which may lead to a non-invasive and safer way of testing unborn babies for genetic diseases.
The researchers hope to develop new testing methods
A team from the Chinese University of Hong Kong have identified foetal DNA in a mother's blood - which can now potentially be examined for problems.
Scientists are trying to find ways of bettering existing pre-natal tests, which carry a risk of miscarriage.
The study appears in Proceedings of the National Academy of Sciences.
At the moment, pregnant women can be given amniocentesis, carried out at 15 to 18 weeks' gestation, which involves using a needle to collect fluid from the amniotic sac surrounding the foetus.
However the test causes a miscarriage in around one in 100 cases.
Another check available is chorionic villus testing, which involves taking a small sample of placental tissue at 10 to 12 weeks.
This test also carries a risk of miscarriage in up to one per cent of cases.
It has been known for some time that a low concentration of foetal DNA is present in the blood plasma of pregnant women.
But it is hard to identify, and scientists around the world are seeking ways of locating it easily.
The team at the Chinese University were investigating if there were differences between the chemical behaviour of foetal and maternal DNA.
Focussing on a gene called maspin, they found that a particular type of chemical modification, methylation, occurs at much higher levels in maternal DNA than foetal DNA.
Unmethylated foetal DNA was detected in maternal blood plasma throughout pregnancy, but disappeared within 24 hours of delivery, indicating it is specific to pregnancy.
Writing in PNAS, the team led by Dr Stephen Chim said they had shown it was possible to find genetic markers for foetal DNA in maternal blood.
They say this could therefore provide the basis of new non-invasive ways of diagnosing conditions in foetuses, and monitoring development throughout pregnancy.
"We believe this marks a significant step forward," the researchers said.
Dr David Liu, director of the foetal care unit at City Hospital in Nottingham, has also been investigating ways of identifying foetal cells in the mother's blood.
He told the BBC News website: "The team in Hong Kong have found a way of picking out what is baby and what is mother, by looking at a molecular biology level.
"The next step is how this works in the clinical arena.
"Although cells can be picked out, the researchers need to find out whether it will be applicable for testing for the various conditions we are looking at."
Dr Liu added: "The tests we have at the moment are invasive, and carry a risk of miscarriage.
"Obviously, if we can avoid that, it would be better."
A spokesman for the charity Life expressed concern about how new technology would be used.
"Prenatal genetic testing has proved to be a decidedly mixed blessing, and is increasingly being used to promote an unabashedly eugenic agenda, involving the arbitrary destruction of any life seen as imperfect or burdensome on the rest of society.
"Already 96% of unborn children diagnosed with Down's syndrome are aborted in the womb, while abortions are routinely carried out for relatively minor impairments such as club foot and cleft palate.
"Once life was seen as inviolable for its own sake: now our ethic of life is consumer-led, based on utilitarian notions of usefulness and convenience."