http://www.medpagetoday.com/OBGYN/Pregnancy/tb/4991
The article is about detecting down's syndrome, but the methodology looks interesting. Perhaps it would be hard to get enough fetal dna in the mother's blood sample to test...
Here are the relevant paragraphs -
The test used the small amounts of fetal DNA that cross the placenta and circulate in the mother's blood plasma. The researchers discovered a way to distinguish maternal from fetal free DNA by measuring the ratio of alleles at the site of single nucleotide polymorphisms on different chromosomes.
Current screening tests for Down's syndrome, such as such as amniocentesis and chorionic villus sampling, have a small but real risk of miscarriage. Amniocentesis is generally done at 15 to 18 weeks. Chorionic villus sampling (CVS) is done at 10 to 12 weeks.
"Development of non-invasive tests that yield diagnostic results would be a useful advancement in prenatal care," Dr. Dhallan and colleagues said. "Venipunctures are done routinely in clinical settings and present little risk to the mother and fetus."
Their results are promising and open a new era in prenatal diagnosis though they need to be replicated in a larger trial, according to an editorial by Alexandra Benachi, M.D., of the Université Paris-Descartes in Paris, and Jean-Marc Costa, Ph.D., of the Hôpital Américain de Paris in Neuilly, France.
Compared with amniocentesis or newborn reports from the clinical sites, the blood test results were accurate for 58 of 60 samples, including two correctly identified cases of trisomy 21. However, there was one false positive and one false negative.
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