Context Noninvasive prenatal diagnostic tests using free fetal DNA provide an
alternative to invasive tests and their attendant risks; however, free fetal
DNA exists in the maternal circulation at low percentages, which has hindered
development of noninvasive tests.
Objective To test the hypothesis that using formaldehyde to reduce cell lysis
could increase the relative percentage of free fetal DNA in samples of maternal
Design, Setting, and Patients The first phase of the study was conducted from January through February
2002 at a single US clinical site; 2 samples of blood were collected from
each of 10 pregnant women, and the percentage of free fetal DNA in formaldehyde-treated
and untreated samples was determined. The second phase of the study was conducted
from March 2002 through May 2003, and measured the percentage of free fetal
DNA in 69 formaldehyde-treated samples of maternal blood obtained from a network
of 27 US clinical sites in 16 states.
Main Outcome Measure Percentage of free fetal DNA in samples of maternal blood.
Results In the first phase of the study, the mean percentage of free fetal DNA
in the untreated samples was 7.7% (range, 0.32%-40%), while the mean percentage
of free fetal DNA in the formaldehyde-treated samples was 20.2% (range, 1.6%-40%)
(P = .02 for difference). In the second phase, a
median of 25% (range, 3.1% to >50%) free fetal DNA was obtained for the 69
formaldehyde-treated maternal blood samples. Approximately 59% of the samples
in this study had 25% or greater fetal DNA, and only 16% of the samples had
less than 10% fetal DNA. In addition, 27.5% of the samples in this study had
50% or greater fetal DNA.
Conclusion Addition of formaldehyde to maternal blood samples, coupled with careful
processing protocols, increases the relative percentage of free fetal DNA,
providing a foundation for development of noninvasive prenatal diagnostic
tests to distinguish fetal DNA from maternal DNA in the maternal circulation.