- With Mayo Clinic obstetrician and medical editor-in-chief
Roger W. Harms, M.D.
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Roger W. Harms, M.D.
Roger W. Harms, M.D.
"Nothing helps people stay healthy more than the power of real knowledge about health." — Dr. Roger Harms
As medical director of content, Dr. Roger Harms is excited about the potential for Mayo Clinic's health information site to help educate people about their health and provide them the tools and information to live healthier lives.
The Auburn, Neb., native has been with Mayo Clinic since 1981 and is board certified in obstetrics and gynecology. Dr. Harms is a practicing physician and associate professor of obstetrics and gynecology, and his specialty areas include office gynecology, high-risk obstetrics and obstetrical ultrasound.
From 2002 to 2007, Dr. Harms was director for education at Mayo Clinic, Rochester, Minn. Dr. Harms was the 1988 Mayo Medical School Teacher of the Year and served as associate dean for student affairs and academic affairs. He is the co-author of the "Mayo Clinic Model of Education." In 2008, Dr. Harms was presented the Distinguished Educator Award, Mayo Clinic, Rochester.
Dr. Harms is vice chair of the Department of Obstetrics & Gynecology and medical editor of the Pregnancy section on this website. In addition, Dr. Harms is editor-in-chief of the "Mayo Clinic Guide to a Healthy Pregnancy" book, a month-by-month guide to everything a woman needs to know about having a baby.
"My medical education experience has grown out of a love of teaching, and that is what this site is about," Dr. Harms says. "If any visitor to this site makes a more informed and thus more comfortable decision about his or her health because of the information we provide, we are successful."
Healthy pregnancy (18)
- Breast-feeding while pregnant: Is it safe?
- X-ray during pregnancy: Is it safe?
- Allergy medications and pregnancy: What's safe?
- see all in Healthy pregnancy
First trimester (4)
- Implantation bleeding: Normal in early pregnancy?
- Down syndrome blood test: How does it work?
- Nausea during pregnancy: A good thing?
- see all in First trimester
Second trimester (1)
- Fundal height: An accurate sign of fetal growth?
Third trimester (1)
- Hypnobirthing: How does it work?
Pregnancy problems (9)
- Pregorexia: A legitimate problem during pregnancy?
- Chickenpox and pregnancy: What are the concerns?
- Low amniotic fluid: How is it treated?
- see all in Pregnancy problems
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Question
Down syndrome blood test: How does it work?
How does the Down syndrome blood test work?
Answer
from Roger W. Harms, M.D.
The Down syndrome blood test is a new prenatal screening test for women at high risk of having a baby who has Down syndrome. The test is used to evaluate your risk of carrying a baby who has Down syndrome. In some cases, the Down syndrome blood test can help you avoid testing that's more invasive.
During the Down syndrome blood test — which can be done as early as week 10 of pregnancy — a maternal blood sample is taken and sent to a lab. At the lab, fetal DNA circulating within the blood is analyzed for extra chromosome 21 sequences. A higher than expected number of chromosome 21 sequences indicates an increased risk of trisomy 21, the most common cause of Down syndrome. Trisomy 21 occurs when a person has three copies of chromosome 21, instead of the usual two copies, in all of his or her cells. The Down syndrome blood test doesn't specifically address other genetic or chromosomal conditions or other rare causes of Down syndrome. Your health care provider will be notified, however, if extra sequences of chromosome 13 (trisomy 13) or chromosome 18 (trisomy 18, also called Edwards syndrome) are found. Typically, test results are available within two weeks.
If a traditional prenatal screening test — such as first trimester screening or the quad screen — indicates that you're at high risk of carrying a baby who has Down syndrome, a more invasive test is typically offered to confirm the diagnosis. For example:
- Amniocentesis. During this procedure, a sample of the fluid that surrounds and protects the baby during pregnancy (amniotic fluid) is removed from the uterus for testing.
- Chorionic villus sampling (CVS). During CVS, a sample of the wispy projections that make up most of the placenta (chorionic villi) are removed from the placenta for testing.
Amniocentesis and CVS both carry a slight risk of miscarriage. You might be able to avoid amniocentesis or CVS, however, by taking the Down syndrome blood test. If the Down syndrome blood test results are normal, you might not need further testing. If the Down syndrome blood test detects a high risk of trisomy 21, amniocentesis or CVS will be offered to confirm the results.
If you have risk factors for having a baby who has Down syndrome — you're an older mother or you have a family history of Down syndrome — ask your health care provider about the Down syndrome blood test. Also ask about the blood test if you've gotten positive or worrisome results from another prenatal screening test. Your health care provider or a genetic counselor can help answer any questions you might have and discuss what the results might mean for you and your family.
Next questionNausea during pregnancy: A good thing?
- Chiu RWK, et al. Non-invasive prenatal assessment of trisomy 21 by multiplexed maternal plasma DNA sequencing: Large scale validity study. British Medical Journal. 2011;342:c7401.
- Shulman LP. One small step and one giant leap for noninvasive prenatal screening: An editorial. American Journal of Obstetrics and Gynecology. 2011;204:183.
- Ehrich M, et al. Noninvasive detection of trisomy 21 by sequencing of DNA in maternal blood: A study in a clinical setting. American Journal of Obstetrics and Gynecology. 2011;204:205e1.
- Palomaki GE, et al. DNA sequencing of maternal plasma to detect Down syndrome: An international clinical validation study. Genetics in Medicine. 2011;13:913.
- Frequently asked questions. Pregnancy FAQ133. Routine tests in pregnancy. American College of Obstetrics and Gynecology. http://www.acog.org/Resources_And_Publications/~/media/For%20Patients/faq133.ashx. Accessed Jan. 11, 2012.
- Down syndrome. National Institute of Child Health & Human Development. http://www.nichd.nih.gov/health/topics/Down_Syndrome.cfm. Accessed Jan. 11, 2012.
- Sehnert AJ, et al. Optimal detection of fetal chromosomal abnormalities by massively parallel DNA sequencing of cell-free fetal DNA from maternal blood. Clinical Chemistry. 2011;57:1042.
- What causes Down syndrome? National Down Syndrome Society. http://www.ndss.org/index.php?option=com_content&task=category§ionid=23&id=60&Itemid=234. Accessed Jan. 11, 2012.
- Wick MJ (expert opinion). Mayo Clinic, Rochester, Minn. Jan. 28, 2012.
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