Instead of trying to separate fetal and maternal DNA, the method described in PNAS counts how many fragments come from each chromosome.

A group of scientists report that they have developed a test that requires only a maternal blood sample to spot chromosomal disorders such as Down syndrome. They note that if the procedure is validated, it would provide a safer option to current methods such as amniocentesis and chorionic villus sampling.

While the ability to separate fetal DNA from a mother’s DNA has been the challenge, the research team developed a method that does not require distinction between maternal and fetal DNA.

First, the group took samples from 12 women with aneuploid pregnancies and six with normal pregnancies and separated the maternal blood into cells and plasma. They then discarded the blood cells, focusing on the liquid plasma’s DNA fragments, which come from both the mom and the fetus. They counted the number of DNA fragments and used DNA sequencing to read each one.

Next, the researchers tallied how many gene fragments originated from each chromosome. Women with Down syndrome pregnancies in the study had more chromosome-21 fragments in their blood than women with normal pregnancies. Other forms of aneuploidy could be detected as well, according to the researchers.

The next step is to repeat the study in a larger number of women. The group expects it will take the new test two to three years to reach the clinic, assuming that the larger trial is successful.

The study, was published online on October 6 in the early edition of the Proceedings of the National Academy of Sciences (PNAS), was developed by researchers at Stanford University, the Howard Hughes Medical Institute, and Lucile Packard Children’s Hospital.

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