Finding out if a fetus has a genetic abnormality at birth is possible using noninvasive prenatal testing (NIPT), also known as noninvasive prenatal screening (NIPS). Little DNA fragments that are circulating in a pregnant woman’s blood are analyzed by this test. These fragments are known as cell-free DNA (cfDNA) because they are free-floating and not contained within cells, in contrast to most DNA, which is located inside a cell’s nucleus. These tiny pieces, which are typically composed of fewer than 200 base pairs (the building blocks of DNA), are produced as cells divide, release their constituent parts into the circulation, and die.
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A combination of the mother’s cells and the placenta’s cells make up the mother’s bloodstream during pregnancy. The tissue in the uterus that connects the fetus to the mother’s blood supply is called the placenta. Throughout the pregnancy, the mother’s circulation is exposed to these cells. The fetus’s DNA and the placental cells’ DNA are often similar. Without endangering the fetus, placental cfDNA analysis offers the possibility of early diagnosis of certain genetic disorders.
The most common use of NIPT is to search for chromosomal abnormalities brought on by an extra or missing copy (aneuploidy) of a chromosome. Trisomy 21, which is caused by an extra chromosome 21, trisomy 18, which is caused by an extra chromosome 18, trisomy 13, which is caused by an extra chromosome 13, and extra or missing copies of the X and Y chromosomes, or the sex chromosomes, are the main conditions that are searched for by NIPT. The test’s accuracy differs depending on the disease.
Additional chromosomal diseases that result from duplicated or missing chromosomal segments may also be screened for during NIPT. The use of NIPT to screen for genetic illnesses resulting from variations in single genes is growing. Researchers anticipate that many more genetic disorders will be able to receive NIPT as genetic testing costs come down and technology advances.
Because NIPT just needs blood to be drawn from the pregnant patient and does not endanger the fetus, it is regarded as noninvasive. Since NIPT is a screening test, it cannot determine with certainty if a fetus has a genetic problem. The test is limited to estimating the relative increase or decrease in risk associated with certain conditions. Sometimes the NIPT results show a lower risk of a genetic abnormality when the baby is truly afflicted, or they show a higher risk of a genetic abnormality when the fetus is genuinely unaffected (false positive) (false negative). Given that NIPT examines both maternal and fetalcfDNA, a genetic disorder in the mother may be identified by the test.
To detect fetal chromosomal abnormalities, there must be sufficient fetal cfDNA in the mother’s circulation. The term “fetal fraction” refers to the percentage of cfDNA derived from the placenta in maternal blood. Fetal fractions usually need to be greater than 4 percent, which usually happens by the ninth week of pregnancy. Low fetal fractions may result in a false negative result or make the test impossible to conduct. Low fetal fractions can be caused by fetal abnormalities, sample mistakes, obesity in the mother, and testing too early in the pregnancy.
There exist several NIPT techniques for analyzing fetal cfDNA. The most popular technique for identifying chromosomal aneuploidy is counting all cfDNA fragments (both fetal and maternal). The fetus has a lower chance of having a chromosomal condition (negative test result) if the percentage of cfDNA fragments from each chromosome is as predicted. The fetus is more likely to have a trisomy condition (positive test result) if the percentage of cfDNA fragments from a certain chromosome is higher than predicted. When a screening test yields a positive result, additional testing—referred to as diagnostic testing as it is used to detect diseases—should be carried out to validate the findings.