There is always genetic material (cell-free DNA) floating in our bloodstreams. When an individual is pregnant, pieces of genetic information from the placenta (cell-free fetal DNA) are released into their bloodstream and mix with their own genetic information. NIPT tests the mixture of DNA to determine if there is a high or low risk that the baby has certain chromosome anomalies. Fetal fraction, or the proportion of DNA in the blood sample that comes from the placenta, can affect the accuracy of an NIPT test.