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What does the NIPT test for

What does the NIPT test for

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What does the NIPT test for? Additional chromosomal diseases caused by missing (deleted) or copied (duplicated) parts of a chromosome may be detected using NIPT. NIPT is now being used to screen for genetic illnesses caused by single-gene variations (variants). Researchers anticipate that as technology advances and the cost of genetic testing drops, NIPT will become available for a greater number of hereditary diseases.

What Does The Nipt Test For

What does the NIPT test for

Noninvasive prenatal testing (NIPT), also known as noninvasive prenatal screening (NIPS), is a technique for estimating the likelihood that a fetus may be born with genetic abnormalities. Small bits of DNA circulating in a pregnant woman’s blood are analyzed in this test. Unlike most DNA, which is located inside a cell’s nucleus, these pieces are free-floating and are referred to as cell-free DNA since they are not contained within cells (cfDNA). When cells die and are broken down, their contents, including DNA, are released into the circulation, these little fragments form. They normally comprise fewer than 200 DNA building blocks (base pairs).

Because it just needs collecting blood from the pregnant mother and poses no risk to the fetus, NIPT is termed noninvasive. Because NIPT is a screening test, it cannot provide a clear answer as to whether or not a fetus has a genetic disease. The test can only tell you whether your chances of developing certain diseases have increased or decreased. When the fetus is genuinely unaffected, NIPT findings may suggest an increased risk for a genetic abnormality (false positive), or when the fetus is actually affected, the results may indicate a lowered risk for a genetic abnormality (false negative) (false negative). Because NIPT analyzes both fetal and maternal cfDNA, the test may detect a genetic condition in the mother.

To detect fetal chromosome abnormalities, there must be enough fetal cfDNA in the mother’s bloodstream. The fetal fraction is the percentage of cfDNA in maternal blood that comes from the placenta. The fetal fraction must be greater than 4% in most cases, which happens around the ninth week of pregnancy. Low fetal fractions can make the test impossible to complete or result in a false negative. Testing too early in the pregnancy, sampling mistakes, maternal obesity, and fetal abnormalities are all reasons for low fetal fractions.

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There are several NIPT methods for fetal cfDNA analysis. The most frequent method for determining chromosomal aneuploidy is to count all cfDNA fragments (both fetal and maternal). If the percentage of cfDNA pieces from each chromosome is as expected, the fetus is less likely to have chromosomal abnormalities (negative test result). If the fraction of cfDNA fragments from a specific chromosome is higher than expected, the fetus is more likely to be born with a trisomy (positive test result). A positive screening result indicates that more testing (referred to as diagnostic testing because it is used to diagnose a condition) is needed to confirm the result.

The mother’s bloodstream carries a mixture of cfDNA from her cells and cells from the placenta throughout pregnancy. The placenta is uterine tissue that connects the mother’s blood supply to the fetus. During pregnancy, these cells are lost into the mother’s bloodstream. The DNA of placental cells and the DNA of the fetus are usually identical. The analysis of cfDNA from the placenta allows for the early diagnosis of some genetic disorders without causing harm to the fetus.

NIPT vs. serum screening vs. diagnostic tests

You may choose to have NIPT, a serum screening test, a diagnostic test, a combination of the tests, or no testing at all. Here are the most important differences between the tests:

NIPT

  • Can be performed as early as nine weeks
  • Tells you the chances of your baby having a chromosomal abnormality such as trisomy 21 (Down syndrome) and—depending on the type of NIPT you choose—many more conditions
  • Screens for fetal sex
  • Done via a maternal blood sample from the mother’s arm
  • Does not cause miscarriages
  • Can require diagnostic testing to confirm a positive result (a “positive result” likely means the baby is affected)

Serum screening

  • Can be performed as early as 10 weeks
  • Done via a maternal blood sample from the mother’s arm
  • Does not cause miscarriages
  • Tells you the chance that your baby could have trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and when drawn after 15 weeks, open neural tube defects (such as spina bifida)
  • Sometimes show a high risk even when the baby does not have one of these problems

NOTE: The American College of Obstetricians and Gynecologists recommends that women with a “high risk” maternal serum screening result be offered diagnostic testing.1 Women with a “low risk” result often choose not to have diagnostic testing.

Diagnostic tests

  • Can be performed as early as 10 weeks (CVS) or 15 weeks (amniocentesis)
  • Tell you with greater than 99% accuracy whether your baby is affected or is not affected with Down syndrome or trisomy 18
  • Tell you with greater than 90% accuracy whether your baby is affected with an open neural tube defect
  • Can test for other genetic disorders when additional risks are identified in a patient’s history
  • Are estimated to cause miscarriage in 1 in 300 to 1 in 500 pregnancies for amniocentesis and up to 1 in 100 with CVS

NOTE: Not even diagnostic testing can show all birth defects or genetic diseases. No test is perfect: even when all the results of diagnostic testing are normal, all pregnancies still have approximately a 3-5% risk of birth defects.

Screening of the carrier

While NIPTs, serum screening, and prenatal diagnostic tests reveal your baby’s genetic health, carrier screening identifies your and your partner’s carrier status and helps to establish if you and your spouse are at risk of passing on a genetic condition like cystic fibrosis (which affects about 1 in 3,500 babies born in the US).

These tests are done on a blood sample taken from your arm and can be done before or during pregnancy.

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