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Noninvasive prenatal testing (NIPT) can help detect certain chromosomal abnormalities in a developing fetus.
Most DNA is contained within cells, but a small amount circulates freely in the bloodstream. During pregnancy, a small percentage of cell-free DNA in a woman’s blood is from the placenta and usually matches the DNA of the fetus. With NIPT, cell-free fetal DNA can be examined for evidence of aneuploidy (an extra or missing chromosome). For example, NIPT can be used to look for Down syndrome, which is caused by an extra copy (trisomy) of chromosome 21.
When Is NIPT Used?
Noninvasive prenatal testing is not a routine prenatal test, which means it is not automatically performed during pregnancy. It is usually offered when a pregnant woman has an increased risk of having a child with aneuploidy. The American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) recommend the test when
A woman will be aged 35 years or older at the time of delivery
A routine prenatal test result is positive for aneuploidy
A woman has a history of pregnancy with fetal trisomy
An ultrasound shows a fetal abnormality that could be caused by aneuploidy
A parent has a history of certain chromosomal abnormalities
The ACOG and the SMFM do not currently recommend NIPT as a first screening test in low-risk or multiple pregnancies. Scientists continue to study NIPT, but its accuracy has not yet been demonstrated in large numbers of women in these groups.
If your doctor recommends NIPT, you will need to have a sample of blood drawn. The test is done after the 10th week of pregnancy, and results are usually available in about a week.
Noninvasive prenatal testing is accurate for detecting trisomy 21 and trisomy 18 (Edwards syndrome) in high-risk pregnancies but is less reliable for trisomy 13 (Patau syndrome) and sex chromosome abnormalities like Turner syndrome and Klinefelter syndrome.
Even though NIPT is very good for detecting certain trisomies, a positive result is not used for diagnosis. This is because in certain conditions, cell-free fetal DNA may not exactly match the DNA of the fetus. If you have a positive result, it is usually recommended that your doctor perform a follow-up test to confirm the result.
Cell-Free DNA and Cancer
In patients with cancer, some cell-free DNA comes from cancer cells that have died and released their mutated DNA into the bloodstream. Recently, scientists have been studying ways to use this tumor DNA to detect and monitor cancers.
A study in the July 14, 2015, issue of JAMA reports on how NIPT was used to detect maternal cancer. For some women, an abnormal NIPT result was due to an undiagnosed cancer.
The authors of this study followed up the results of NIPT in a way that is not routinely done. The NIPT results themselves were not diagnostic for cancer, and NIPT is not currently used to screen for maternal cancer. Further research is needed to determine the clinical importance of this finding.
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Sources: Bianchi DW, Chudova D, Sehnert AJ, et al. Incidental detection of occult maternal malignancies by noninvasive prenatal testing. JAMA. doi: 10.1001/jama.2015.7120.
National Coalition for Health Professional Education in Genetics
American College of Obstetricians and Gynecologists
Society for Maternal-Fetal Medicine
Thompson AE. Noninvasive Prenatal Testing. JAMA. 2015;314(2):198. doi:10.1001/jama.2015.7655
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