A highly specific and sensitive NIPT method has recently become available as an alternative for prenatal screening tests that are currently in use. The NIPT method measures the level of circulating cell-free fetal DNA (cfDNA) present in maternal plasma to identify fetal aneuploidies, including Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13). Fetal DNA represents approximately three to six percent of the total DNA in the maternal circulation. cfDNA typically can be detected in maternal plasma as early as the fifth postmenstrual week and almost always detected by the ninth postmenstrual week. Normally the percentage of fetal DNA increases with increasing gestational age.
One of the major challenges with identifying cfDNA is separating fetal DNA from maternal DNA . At present, there are two major techniques for isolating fetal DNA from maternal DNA: Massively parallel signature sequencing (MPSS) and directed DNA analysis.