Simple Test Could Detect Down's Syndrome
Some women are offered an alternative test -- known as chorionic villus sampling (CVS) -- which can be performed much earlier than an amniocentesis, from around 12 weeks, where a tiny quantity of tissue can be taken from the placenta. However, this too carries a risk of miscarriage.
The hope is the new technique will be easier and safer. Scientists at the Chinese University of Hong Kong identified three women who were carrying fetuses already known to have the most common form of Down's syndrome, and 10 others who were carrying babies with normal chromosomes.
At 12 weeks gestation, doctors took a tiny sample of each mother's blood. Then they took another sample at 15 weeks, after some of the women had undergone CVS testing. The reason for this was that CVS could introduce fetal cells into the mother's blood during the procedure. The scientists wanted to see if the same cells were already there before the pregnant women underwent any tests.
Using a technique called fluorescence in-situ hybridization (FISH) -- where fluorescent markers are used to paint a picture of the part of the chromosome under investigation -- the researchers were able to pinpoint fragments of fetal DNA.
In all three Down's syndrome cases, they were able to detect the chromosomal abnormalities from the mother's blood early on in the pregnancy. After each woman had CVS testing, they checked the samples again and found the same defects.
"These results indicate that these cells were present in maternal plasma before the invasive procedure," the researchers write. "We have shown that prenatal detection can be accomplished by FISH analysis of fetal cells harvested from maternal plasma. The procedure is simple, and our data suggest future large-scale trials should be initiated to assess the diagnostic accuracy of this method."
Despite the fears of miscarriage, tests like amniocentesis and CVS are relatively safe, says Deborah Driscoll, MD, associate professor of medicine at the University of Pennsylvania's department of obstetrics and gynecology in Philadelphia. But because of the miscarriage fears, doctors are looking to make more options available. That is what's motivating investigators like the ones here to look for tests that are easier to do and come with lower risks than those commonly used today.