Non-Invasive Prenatal Testing involves looking at cell-free fetal (cffDNA) in the mothers blood. This is genetic material that is released by the and circulates in a woman's blood during pregnancy. CffDNA generally reflects the genetic makeup of the developing baby (fetus). The technology employed in this test detects abnormalities in fetal DNA after it is purified from the pregnant woman's blood.
CffDNA is detectable in a pregnant woman's blood in very small quantities from the later stages of the first trimester. Levels then increase as the pregnancy progresses.
The test can accurately identify chromosome disorders in a developing fetus, including the presence of extra chromosomes (trisomies) such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). The extra genetic material present in these conditions affects the development of the fetus and causes characteristic signs, symptoms, and complications in later life.
Down syndrome is the most common of the three trisomies detected by NIPT and is a condition that can vary significantly in severity from person to person. Edwards syndrome and Patau syndrome are more rare and more severe, with most affected babies dying within weeks or months of birth. This test may be used to identify other rare conditions resulting from an extra chromosome or missing piece of chromosome (microdeletion).
Non-Invasive Prenatal Testing (NIPT) may also detect an extra sex chromosome if this abnormality is present. One example is , resulting from two X chromosomes and one Y chromosome. For more on this and other rare chromosome disorders, see the Related Pages tab.
Current routine prenatal testing in the UK includes the first trimester combined screen and the second trimester maternal serum screen. These achieve a detection rate of between 80-90% for Down’s syndrome. Studies have shown that NIPT for cffDNA can be more specific and sensitive than current routine tests in high-risk women, possibly achieving detection rates as high as 99%. It also generates far fewer false positive results.
cffDNA analysis can also be used to identify the blood group of a fetus. This is used to help manage pregnancies where the mother has a particular Rhesus blood type called RhD-negative.
It is important to keep in mind that NIPT is a screening test, not a diagnostic test. If there are abnormal findings in routine prenatal testing or NIPT then more invasive testing, such as chorionic villus sampling (CVS) between 10 and 15 weeks of pregnancy or an amniocentesis procedure between 15 and 20 weeks of , may be required to confirm the diagnosis.