ABSTRACT
Non-invasive prenatal testing (NIPT) was first made possible in the 1970s with the introduction of two-dimensional fetal imaging. Tests for indirect markers associated with, but not 100% predictive of, fetal chromosomal anomalies, such as alpha-fetoprotein, pregnancy-associated plasma protein A, and the free beta subunit of human chorionic gonadotropin, also became available. The current first trimester screen (FTS) calculates the risk of fetal aneuploidy based on indirect biochemical markers, ultrasound measurements at different weeks of fetal gestation, and maternal age. FTS has an aneuploidy detection rate of 85%–95% with a 5% false-positive rate [1]. Invasive prenatal testing is recommended to more accurately determine the chromosomal status of the fetus if the calculated risk value of aneuploidy is greater than 1/100 to 1/270, depending on the institutional policy and the combination of markers studied. The new generation of NIPT utilizes fetal DNA found in the maternal bloodstream to check for aneuploidy instead of relying on a proxy marker associated with aneuploidies [2]. Since the first description of circulating free placental DNA (cfpDNA) within the maternal bloodstream, there have been many improvements in its detection [3-7]. As a consequence, NIPT has a higher specificity and sensitivity than the FTS [8,9].
