What aspects of the fetus does non-invasive prenatal DNA testing (NIPT) primarily assess?
Aug 18, 2021
Source: Cainiu Health
Dr. Zhang Xuemei
Introduction
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 to analyze cell-free fetal DNA fragments circulating in her bloodstream—hence the term “non-invasive DNA testing.” The detection accuracy of NIPT exceeds 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 around week 12 of pregnancy, when prenatal registration occurs. 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 one extra or one missing chromosome constitutes a chromosomal abnormality—all of which can adversely affect fetal development and are considered pathological. NIPT serves as a prenatal screening tool for detecting such fetal chromosomal abnormalities, with highest accuracy achieved for three specific chromosomes: chromosome 21, chromosome 18, and chromosome 13. Abnormalities involving these chromosomes include trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome). The detection accuracy for these three conditions is notably high—ranging from 90% up to 99%.
In most cases, clinicians report an accuracy exceeding 95% for these three chromosomal conditions. In contrast, conventional prenatal screening—commonly known as “Down syndrome screening”—relies on combined first- and second-trimester assessments; its overall detection rate reaches only 60–70%. Moreover, this traditional method does not analyze fetal cell-free DNA fragments.
Instead, it measures certain biochemical markers in maternal serum, integrating these results with maternal age and other confounding variables to calculate an estimated risk probability. From a mechanistic perspective, it becomes clear why NIPT offers significantly higher diagnostic accuracy.
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 (umbilical blood sampling)—are recommended to definitively assess chromosomal status and guide decisions regarding continuation of the pregnancy.
