What aspects of the fetus does non-invasive prenatal DNA testing (NIPT) primarily assess?
Sep 03, 2021
Source: Cainiu Health
Dr. Zhang Xuemei
Introduction
Non-invasive prenatal DNA testing (NIPT) is a commonly used non-invasive prenatal genetic screening method. It primarily involves drawing a peripheral blood sample from the pregnant woman to analyze cell-free fetal DNA fragments circulating in her bloodstream—hence the term “non-invasive DNA testing.” NIPT has an accuracy rate exceeding 95%. However, if the NIPT result indicates a high risk, further invasive prenatal diagnostic testing is still recommended.
Non-invasive prenatal DNA testing (NIPT) is commonly referred to as non-invasive prenatal genetic screening. It primarily involves drawing a peripheral blood sample from the pregnant woman—typically during the routine venous blood draw performed at approximately 12 weeks’ gestation when establishing the prenatal care record. Using this maternal blood sample, we analyze cell-free fetal DNA fragments circulating in the mother’s bloodstream; this procedure is known as NIPT.
The human genome comprises 23 pairs of chromosomes; having either an extra or missing chromosome constitutes a chromosomal abnormality, all of which can adversely affect fetal development and are therefore considered abnormal. NIPT serves as a prenatal screening tool for detecting such fetal chromosomal abnormalities. Its highest accuracy is achieved for three specific chromosomes: chromosome 21, chromosome 18, and chromosome 13. Abnormalities involving these chromosomes—namely trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome)—can be detected with high sensitivity, achieving accuracy rates of up to 90%–99%.
In clinical practice, NIPT is generally reported to achieve detection accuracy exceeding 95% for these three chromosomal conditions. In contrast, traditional prenatal screening—commonly termed “Down syndrome screening”—relies on combined first- and second-trimester assessments (early and mid-pregnancy screening, respectively). Even when integrated, its overall detection rate reaches only 60–70%, and it does not directly analyze fetal cell-free DNA fragments.
Instead, conventional screening measures certain biochemical markers in maternal serum and incorporates maternal age and other confounding variables to calculate an estimated risk probability. From a mechanistic standpoint, it becomes clear why NIPT offers superior accuracy compared to traditional serum screening.
Nevertheless, NIPT remains a screening—not a diagnostic—test. If NIPT yields a high-risk result, further confirmatory prenatal diagnostic procedures—such as amniocentesis or cordocentesis (percutaneous umbilical blood sampling)—are recommended to definitively assess fetal chromosomal status and guide subsequent decisions regarding continuation of the pregnancy.
