"In the first phase of the study, the mean (average) percentage of free fetal DNA in the untreated samples was 7.7 percent, while the mean percentage of free fetal DNA in the formaldehyde-treated samples was 20.2. percent. In the second phase, a median (half-way point) of 25 percent free fetal DNA was obtained for the 69 formaldehyde-treated maternal blood samples. Approximately 59 percent of the samples in this study had 25 percent or greater fetal DNA, and only 16 percent of the samples had less than 10 percent fetal DNA. In addition, 27.5 percent of the samples in this study had 50 percent or greater fetal DNA."

The authors conclude, "When samples have a high percentage of free fetal DNA, the difference between the expected ratio of the chromosomes for a healthy fetus and that for an abnormal fetus is greater, which makes it easier to diagnose chromosomal abnormalities," and suggest that their methods "for increasing the percentage of free fetal DNA provide a solid foundation for the development of a noninvasive prenatal diagnostic test."

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Contact: Susan Higgins
410-715-2111
JAMA and Archives Journals
2-Mar-2004