Noninvasive Prenatal Tests Detect More Than 80 Percent of Chromosomal Abnormalities

Hand with Ring on Pregnant BellyNoninvasive prenatal testing methods detect 83.2 percent of chromosomal abnormalities normally detected by invasive diagnostic testing strategies, says a new study to be presented at the annual meeting of the Society for Maternal-Fetal Medicine, The Pregnancy Meeting, in New Orleans on February 6, 2014.

Prenatal testing refers to a number of tests performed during pregnancy to detect problems in an unborn baby. The most common invasive prenatal tests include chorionic villus sampling (CVS) and amniocentesis. CVS involves removing some chorionic villi cells from the placenta. Amniocentesis involves the collection of the amniotic fluid. As invasive tests, both CVS and amniocentesis increase the risk of miscarriage and stillbirth.

In contrast to invasive prenatal testing, noninvasive prenatal testing involves taking a blood sample from the mother rather than extracting fluid or cells from the fetus. This ensures that no harm is done to either the baby or the mother. It is a fairly simple procedure and does not involve the use of needles to extract embryonic fluid from the womb. The same method is also used in an At-Home prenatal paternity test that can be taken easily by both mother and father for various medical reasons. Noninvasive prenatal testing (NIPT), or noninvasive prenatal diagnosis (NIPD), uses a sophisticated blood test that examines fetal DNA in the maternal bloodstream to determine whether the developing baby is at risk for Down syndrome, extra sequences of chromosome 13 (trisomy 13), extra sequences of chromosome 18 (trisomy 18), or a sex chromosome abnormality such as Turner syndrome. The risks associated with NIPT are much lower than with invasive methods.

In the present study entitled “Rare Chromosome Abnormalities Detected by Current Prenatal Screening Compared to Expected Performance using Non-Invasive Prenatal Testing (NIPT),” the researchers discovered that noninvasive prenatal testing detected 83.2 percent of chromosomal abnormalities detected by invasive methods. NIPT did not detect less common problems.

Furthermore, noninvasive prenatal testing detected more chromosomal abnormalities in older women over the age of 40 compared to younger women. Babies born to older mothers have an increased risk for trisomy 13, 18, or 21. Noninvasive tests failed to detect problems in 25 percent of younger women.

Comments study author Mary Norton, M.D., professor and vice chair for Clinical and Translational Genetics, Department of Obstetrics, Gynecology and Reproductive Sciences at the University of California, San Francisco:

“In prenatal genetic testing, patient preferences are really the most important driver. With this test, the patient makes a tradeoff between NIPT, which is noninvasive and detects most, but not all chromosome abnormalities – and is somewhat better in older women – and amniocentesis or CVS, which detect more chromosome abnormalities [8 to 25 percent more, depending on age] but with a small risk of miscarriage due to the procedure.

“For an older woman, detecting 83 percent with the noninvasive test may be good enough, while for a 25-year-old, failing to detect 25 percent [which may include rare aneuploidies not usually associated with age] may be of concern.”

The researchers do caution that a detection rate of over 80 percent may be good enough for an older mother but that the lower detection rate among younger women may be more of a concern.


Noninvasive prenatal testing:
Noninvasive prenatal testing detects more than 80 percent of chromosomal abnormalities:

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