Prenatal cell-free DNA testing, also known as non-invasive prenatal testing (NIPT), is a relatively new blood test taken in the first trimester of pregnancy to determine a fetus’s risk for chromosomal abnormalities, including Down syndrome (trisomy 21), trisomy 13 and 18 and sex chromosome abnormalities, such as Turner syndrome. The test screens fetal DNA taken from a blood sample given by the mother, instead of screening samples extracted from the uterus or placenta—which is why it's considered non-invasive.
The test is highly accurate—it has a 99 percent accurate detection rate and very low rate of false positives—but it’s a screening test, not a diagnostic test. In other words, NIPT can’t definitively tell you whether or not your baby has Down syndrome or another chromosomal abnormality. It can only tell you whether there’s a high or low probability of one. If the test says there’s a high probability, you may want additional, invasive testing, such as an amniocentesis or chorionic villus sampling (CVS) to help confirm or deny the diagnosis. Some moms-to-be prefer NIPT before deciding to have an amnio or CVS because it doesn’t pose any risk to baby, while invasive tests do have risks associated with them.
The test can be performed as early as 10 weeks of pregnancy and is safe for most women, regardless of age. Note, though, that given the limitations of NIPT, the American College of Obstetricians and Gynecologists (ACOG) still recommends conventional screening methods as a first-line test for women with low-risk pregnancies. NIPT is not recommended for women pregnant with multiples.
If you’re considering NIPT, talk to your doctor to learn more. Only you can decide whether you should get the test. For even more information, you can request a referral to a genetics counselor before making prenatal testing decisions. A genetics counselor can help you evaluate your personal risk factors and risk tolerance to help you make the right choices for your family.
Expert source: Siobhan Dolan, MD, professor of ob-gyn at Albert Einstein College of Medicine and medical advisor to the March of Dimes.
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