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Professional resources - FAQ

What is a trisomy?

Humans have 23 pairs of chromosomes, which are strands of DNA and proteins that carry genetic information. A trisomy is a chromosomal condition that occurs when there are three copies of a particular chromosome instead of the expected two.

Trisomy 21 is due to an extra copy of chromosome 21 and is the most common trisomy at the time of birth. Trisomy 21 causes Down syndrome, which is associated with mild to moderate intellectual disabilities and may also lead to digestive issues and congenital heart defects.1 It is estimated that trisomy 21 is present in one out of every 700 newborns.

Trisomy 18 is due to an extra copy of chromosome 18. Trisomy 18 causes Edwards syndrome and is associated with a high rate of miscarriage. Infants born with trisomy 18 often have congenital heart defects as well as various other medical conditions, shortening their lifespan. It is estimated that trisomy 18 is present in approximately one out of every 5,000 newborns.

Trisomy 13 is due to an extra copy of chromosome 13. Trisomy 13 causes Patau Syndrome and is associated with a high rate of miscarriage. Infants born with trisomy 13 usually have severe congenital heart defects and other medical conditions. Survival beyond the first year is rare. It is estimated that trisomy 13 is present in approximately one out of every 16,000 newborns.

Harmony detects trisomies of chromosomes 13, 18, and 21 in the fetus, but does not rule out all fetal abnormalities, which vary in severity based upon the individual finding.

What will the Harmony Prenatal Test tell me and my provider?

The Harmony Prenatal Test determines the risk of three fetal trisomies by measuring the relative amount of chromosomes in maternal blood.

Why were my test results not reported back to my doctor?

In some cases, patients will not receive a result from the Harmony test due to low levels of fetal DNA in the sample or other factors.