Patent ID: 8450061

Claim:
A method for determining the amount of fetal nucleic acid in a sample comprising: (a) contacting under amplification conditions a nucleic acid sample from a pregnant human subject, which sample nucleic acid contains extracellular nucleic acid comprising fetal nucleic acid and maternal nucleic acid, the combination of the fetal species and the maternal species comprising total nucleic acid in the sample, with: (i) a first set of amplification primers that specifically amplify a first region in sample nucleic acid comprising a feature that (1) is present in the fetal nucleic acid and is not present in the maternal nucleic acid, or (2) is not present in the fetal nucleic acid and is present in the maternal nucleic acid, (ii) a second set of amplification primers that amplify a second region in the sample nucleic acid allowing for a determination of total nucleic acid in the sample, wherein the first region and the second region are different, and (iii) one or more inhibitory oligonucleotides, each comprising a nucleotide sequence complementary to a nucleotide sequence in the second region, wherein the one or more inhibitory oligonucleotides (1) hybridize to the second region but are not extended and (2) reduce the amplification of the second region; thereby generating fetal nucleic acid amplification products and total nucleic acid amplification products, wherein the total nucleic acid amplification products are reduced relative to total amplification products that would be generated if no inhibitory oligonucleotide was present, whereby the total nucleic acid amplification products do not dominate the fetal nucleic acid amplification products; (b) separating the fetal nucleic acid amplification products and total nucleic acid amplification products, thereby generating separated fetal nucleic acid amplification products and total nucleic acid amplification products; and (c) determining the fraction of the fetal nucleic acid in the sample based on the amount of each of the separated fetal nucleic acid amplification products and total nucleic acid amplification products.