A non-invasive test for prenatal diagnosis based on fetal DNA present in maternal blood: a preliminary study.

Background: Use of free fetal DNA to diagnose fetal chromosomal abnormalities has been hindered by the inability to distinguish fetal DNA from maternal DNA. Our aim was to establish whether single nucleotide polymorphisms (SNPs) can be used to distinguish fetal DNA from maternal DNA-and to determine the number of fetal chromosomes-in maternal blood samples.

Methods: Formaldehyde-treated blood samples from 60 pregnant women and the stated biological fathers were analysed.

Methods to increase the percentage of free fetal DNA recovered from the maternal circulation.

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 blood.

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.