Non-invasive prenatal testing
NIPT testing is a form of noninvasive prenatal genetic testing screening that determines the risk of a fetus being born with specific genetic conditions.
The blood of a pregnant woman contains very small fragments of her unborn baby’s DNA, which due to their free-floating nature are known as cell-free DNA (cfDNA). These cells are shed from the placenta during pregnancy and are, for the most part, identical to the DNA of the fetus. This allows for a genetic screening method that can detect with a high degree of accuracy specific genetic changes or mutations that might put the fetus at higher risk for developing certain genetic conditions.
NIPT testing is considered to be an accurate and almost risk-free form of genetic testing. Unlike the more invasive and risky nature of amniocentesis and chorionic villus testing.
It generally occurs early in the first trimester of pregnancy, as early as the tenth week. This is when the fetal fraction, or proportion of fetal cfDNA in the mother’s bloodstream is higher than 4%. Any lower of a fetal fraction and the screening is not as accurate.
What can NIPT testing identify?
NIPT screening can identify common chromosomal disorders caused by either an extra or missing chromosome copy. These disorders include Down syndrome, Trisomy 21 (caused by an extra chromosome 21), Trisomy 18 (caused by a missing chromosome 18), and Trisomy 13 (caused by an extra chromosome 13). It can also identify missing or extra copies of the sex chromosomes – X and Y chromosomes.
The testing may also screen for other chromosomal disorders caused by deleted or duplicated chromosomes. Our understanding of how it can do this is increasing, and with it the accuracy of the testing where these disorders are concerned.
More recently NIPT testing is being used to identify single gene mutations that cause other genetic conditions and syndromes. This will widen the scope of non-invasive testing.
NIPT testing is not a diagnostic test. It can only identify risk for specific conditions, not if a fetus has one. The test also sometimes returns several false positives (identifies risk where there is none), and false negatives (identifies no risk, when there is one). It can also detect or identify risk for a genetic condition in the mother, as the test screens her cfDNA.
A positive result will mean the need for further diagnostic testing to confirm if a fetus has the suspected genetic condition or not.
Genetic counseling
As with any form of genetic screening, genetic counseling is an important support service for anyone undergoing prenatal testing. Genetic counseling can help parents-to-be understand when and if NIPT testing is necessary. Higher maternal age, for example, is considered to be a risk factor for chromosomal abnormalities, and generally, pregnant women over 35 years old would be recommended to consider NIPT testing as a part of prenatal care.
Genetic counseling will help parents-to-be fully understand what NIPT testing is, what it can tell them about the genetic and future health of their unborn child, and how to make sense of the results. They can also help them navigate further genetic testing if NIPT shows a higher risk for a chromosomal abnormality in their child. It may also include the services of a pediatric genetic counselor.
Genetic counseling can also help parents navigate this diagnostic journey, if it becomes necessary, and help guide them emotionally through what may be a very difficult process, as they understand the implications for their child’s health. Genetic counseling should be an integral part of any prenatal genetic screening, analysis, and testing.
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