![]() Generally, the fetal fraction must be above 4 percent, which typically occurs around the tenth week of pregnancy. The proportion of cfDNA in maternal blood that comes from the placenta is known as the fetal fraction. There must be enough fetal cfDNA in the mother’s bloodstream to be able to identify fetal chromosome abnormalities. Because NIPT analyzes both fetal and maternal cfDNA, the test may detect a genetic condition in the mother. In some cases, NIPT results indicate an increased risk for a genetic abnormality when the fetus is actually unaffected (false positive), or the results indicate a decreased risk for a genetic abnormality when the fetus is actually affected (false negative). The test can only estimate whether the risk of having certain conditions is increased or decreased. NIPT is a screening test, which means that it will not give a definitive answer about whether or not a fetus has a genetic condition. NIPT is considered noninvasive because it requires drawing blood only from the pregnant woman and does not pose any risk to the fetus. As technology improves and the cost of genetic testing decreases, researchers expect that NIPT will become available for many more genetic conditions. NIPT is beginning to be used to test for genetic disorders that are caused by changes (variants) in single genes. ![]() NIPT may include screening for additional chromosomal disorders that are caused by missing (deleted) or copied (duplicated) sections of a chromosome. The accuracy of the test varies by disorder. NIPT primarily looks for Down syndrome (trisomy 21, caused by an extra chromosome 21), trisomy 18 (caused by an extra chromosome 18), trisomy 13 (caused by an extra chromosome 13), and extra or missing copies of the X chromosome and Y chromosome (the sex chromosomes). NIPT is most often used to look for chromosomal disorders that are caused by the presence of an extra or missing copy ( aneuploidy) of a chromosome. Analyzing cfDNA from the placenta provides an opportunity for early detection of certain genetic abnormalities without harming the fetus. The DNA in placental cells is usually identical to the DNA of the fetus. These cells are shed into the mother’s bloodstream throughout pregnancy. ![]() The placenta is tissue in the uterus that links the fetus and the mother’s blood supply. These small fragments usually contain fewer than 200 DNA building blocks (base pairs) and arise when cells die off and get broken down and their contents, including DNA, are released into the bloodstream.ĭuring pregnancy, the mother’s bloodstream contains a mix of cfDNA that comes from her cells and cells from the placenta. Unlike most DNA, which is found inside a cell’s nucleus, these fragments are free-floating and not within cells, and so are called cell-free DNA (cfDNA). ![]() This testing analyzes small fragments of DNA that are circulating in a pregnant woman’s blood. Noninvasive prenatal testing (NIPT), sometimes called noninvasive prenatal screening (NIPS), is a method of determining the risk that the fetus will be born with certain genetic abnormalities. ![]()
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