Also, it might shed light on foetal development during pregnancy.
Amniocentesis is an invasive procedure, which is sometimes used by doctors to measure foetal health. It involves inserting a needle into the uterus to obtain a sample of foetal DNA. The procedure carries a risk of injury to the foetus, and a less than one per cent chance of miscarriage.
Other non-invasive procedures that are used for examining a foetus, such as ultrasounds, do not provide a full picture of the baby's development. Therefore, in recent years researchers have created a number of non-invasive procedures to analyse maternal blood for signs of disorders such as Down's syndrome.
Such tests work by picking up DNA and other genetic fragments such as messenger RNA (mRNA) from the placenta, an organ that develops out of the embryo and therefore contains the same genes as the baby itself. During the first five weeks of pregnancy the placenta sheds cells into the mother's bloodstream.
However, genetic fragments from the placenta cannot provide a full picture of foetal development. This is because the pattern of gene activity varies from one organ to another. In other words, the genes that become activated in the baby's eye, for example, might not get switched on in the placenta.
Jill Maron and her colleagues of theTufts-New England Medical Center in Boston, Massachusetts, US, have found evidence that messenger RNA from the foetus itself, not just the placenta, leaks into pregnant women's blood.
"This is a critical step. It could help us better understand how the fetus is developing," Dev Maulik at the Truman Medical Center in Kansas City, Missouri, US, who was not involved in the research, said.
During the study, Maron sampled blood from nine pregnant women before they underwent scheduled Caesarean sections. Immediately following the delivery, the researchers took foetal blood from the umbilical cord. A day later, they took blood samples from the same women, all of whom had delivered healthy babies.
The team determined the presence of 20,000 genes based on the messenger RNA in the three sets of blood samples, using special microarray technology.
The analysis identified mRNA for 157 genes circulating in the women's blood before, but not after, delivery. The mRNA fragments of the genes were also highly prevalent in the foetal blood samples.
Moron has revealed thatmany of the 157 genes are linked to very specific aspects of foetal development, such as the growth of the nervous system and the development of a sense of smell.
She says that fragments of foetal mRNA appear in maternal blood beginning in the second trimester, once the baby starts to produce its own blood.
Moron stressed the need for further research to see if would be possible to regularly examine a pregnant woman's blood for changes in fetal mRNA that signal irregular development of the embryo. For example, abnormal changes in heart and nervous system genes might signal a congenital heart defect or spina bifida, respectively.
"What this does is it broadens what we know is possible," she said, adding that understanding the changes in foetal gene activity might one day lead to ways of treating certain illnesses before birth.
The study is published in the Journal of Clinical Investigation.