Patent ID: 8682594

Claim:
A method for performing prenatal diagnosis of a fetal chromosomal aneuploidy in a maternal sample obtained from a pregnant woman, wherein the maternal sample includes nucleic acid molecules, the method comprising: receiving the maternal sample; sequencing at least a portion of a plurality of the nucleic acid molecules contained in the maternal sample, wherein the sequenced portions comprise a number of sequence tags of sufficient length of determined sequence to be assigned to a chromosome location within a genome; based on the sequencing: determining a length for each of the portion of nucleic acid molecules; determining a first amount of a first chromosome by counting numbers of sequence tags mapping to portions of a first chromosome by using a number of windows of defined length; and determining a second amount of one or more second chromosomes by counting numbers of sequence tags mapping to portions of one or more second chromosomes by using a number of windows of defined length, wherein said counting of sequence tags is within normally or abnormally distributed chromosome portions, and is based on the lengths of the corresponding nucleic acid molecules; calculating a relationship between numbers of sequence tags and GC content associated with sequence tags in a given window and correcting for a higher or lower number of reads resulting from a change in GC content in said window; determining a differential from the first amount and the second amount; determining whether the differential is statistically significant; and correlating a statistically significant result with the presence of a fetal chromosomal aneuploidy on the first chromosome.