Scientists have found a way to maximise the amount of DNA from an unborn baby they can take from the mother's blood.
Better blood tests may be in the offing
They hope the technique will aid the development of more effective non-invasive tests to determine whether a baby has genetic abnormalities.
Current tests, such as amniocentesis, require tissue samples, and pose a small risk to the pregnancy.
The research, published in the Journal of the American Medical Association, was carried out by US company Ravgen.
Being able to identify genetic abnormalities at an early stage not only gives parents the chance to decide whether or not to proceed with the pregnancy, it also alerts medical staff to the need for close monitoring right through to birth.
However, the invasive nature of current tests, which also include chorionic villus sampling and taking blood from the umbilical cord, mean that some women are reluctant to take the risk of having them.
Analysing foetal DNA from a mother's blood sample has been possible for some time. However, its effectiveness has been limited because only a small amount of the DNA makes its way into the mother's blood.
The new technique maximises the amount of DNA that can be recovered by treating the blood samples with a chemical called formaldehyde.
This acts to reduce the amount of blood cells that are destroyed during the process of taking and processing the sample.
If more of the mother's blood cells remain intact, less of her DNA is released into the surrounding fluid, and so it is less able to dilute what little foetal DNA is present there.
The researchers found that blood samples from pregnant women treated with formaldehyde contained an average of 20.2% foetal DNA, compared with just 7.7% in untreated samples.
In a follow-up test, the level of foetal DNA in treated samples was even higher, averaging 25%.
Dr Alan Cameron, a consultant obstetrician at Queen Mother's Hospital, Glasgow, told BBC News Online the research could be highly significant.
He said: "At present we can tell a foetus's blood group from a maternal blood sample, but that is about it.
"Anything that would improve the amount of foetal DNA in a blood sample would open up the possibility of a non-invasive tool for foetal diagnosis. It is something that scientists have been looking at for many years."
Alastair Kent, director of the Genetic Interest Group, said a non-invasive alternative would represent a "terrific breakthrough".
He told BBC News Online: "It would give pregnant women the opportunity to have information on which they could base decisions without potentially putting the future of a healthy pregnancy at risk."