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Thursday, December 5, 2013
Inherited Disorders and Birth Defects
My daughter-in-law is 5 months pregnant and just underwent tests to check the baby for downs syndrome and the tests came back positive. I have heard from several people that these tests could be wrong. Is there any chance that it could be wrong? She had the test where they take fluid from around the baby.
From your description, your daughter-in-law had an amniocentesis - inserting a thin needle into the amniotic sac, obtaining fluid from around the baby which contains the baby's cells and doing a chromosome analysis called a karyotype, which is a diagnostic test. This test is 99.9% accurate. If the test came back positive, meaning the test found that the baby had an extra 21 chromosome, then the baby does have Down syndrome.
The test that you have heard from others that can be wrong is most likely a maternal serum screening test called a "quad screen" or "triple check". These tests look at 3 or 4 types of proteins that have been found to be associated with chromosome problems; the most common one is Down syndrome, also called trisomy 21. Because this blood test is a screening test, not a diagnostic test - it can only tell you about a woman's potential chance or risk to have a baby with Down syndrome. It cannot tell you for sure if the baby will have Down syndrome. In the case of maternal serum screening tests, there is the possibility that the test result is a false positive result. This means that the test result identified the pregnancy as being at risk, but in fact the baby does not have the condition and is normal.
In your daughter-in-law's case, if she had an amniocentesis, this is a diagnostic test and it is very accurate.
If you son and daughter-in-law have not talked to a genetic counselor about the results of the amniocentesis, I would highly recommend that they ask their doctor for a referral to talk to a genetic counselor. This is an area in which they have a lot of expertise. Your son and daughter-in-law can locate a genetics center near where they live through the National Society of Genetic Counselors Resource Center website below.
Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University