Currently several highly specific and sensitive NIPT method are available as an alternative for prenatal screening tests. NIPT methods measure the level of circulating cell-free fetal DNA (cffDNA) present in maternal plasma to identify fetal aneuploidies, including Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13) as well as sex chromosome aneuploidies. cffDNA is genetic material that is released primarily by the placenta and circulates in the mother's blood during the pregnancy. cffDNA typically can be detected in maternal plasma as early as the fifth postmenstrual week and almost always is detected by the ninth postmenstrual week. Normally the percentage of fetal DNA increases with increasing gestational age.
Since fetal DNA represents a small percent of the total DNA in the maternal circulation, a major challenge with identifying cffDNA 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 targeted DNA analysis.
