Noninvasive Prenatal Testing Detects Most Chromosomal Abnormalities

There were 68,990 of 1,324,607 women who tested positive for trisomy 18 or 21 when they underwent prenatal screening between March 2009 and December 2012.

Invasive diagnostic testing with CVS or amniocentesis was performed on 26,059 women who tested positive, and 2,993 were found to have abnormal results. Of those chromosomal abnormalities, 2,489 (83.2%) were abnormalities that would be detectable with NIPT, while 16.8% were less common aneuploidies that would not be detected. The scientists found that more of the abnormal results were detectable in the women over the age of 40, who are at higher risk for trisomy 13, 18, or 21. Conversely, fewer of the abnormalities in younger women would be detected by NIPT, as the risk for common trisomies is lower in this group, while the rare aneuploidies are not typically associated with maternal age.

Mary Norton, MD, one of the study’s authors, said, “While noninvasive prenatal testing with cell free DNA presents some real advantages in accuracy of screening for Down syndrome, as with everything there is a trade-off. Traditional aneuploidy screening with serum and ultrasound markers has higher false positive rates, but in these false positive cases are some fetuses with significant abnormalities that would not be found with NIPT.”

Dr. Norton added, “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% more, depending on age, but with a small risk of miscarriage due to the procedure. For an older woman, detecting 83% with the noninvasive test may be good enough, while for a 25-year-old, failing to detect 25%, which may include rare aneuploidies not usually associated with age, may be of concern.” The study was presented on February 6, 2014, at the Society for Maternal-Fetal Medicine's annual meeting, The Pregnancy Meeting, held in New Orleans (LA, USA).

Related Links:
University of California, San Francisco