March is Trisomy Awareness month so we wanted to pass along a little information to help you understand it better. Testing for the most common types of Trisomies can be done as early as 10 weeks.
What does “Tri” mean? Think tripod, or triathlon, or tricycle. “Tri” is a prefix that means “three”. So, what is a “trisomy?” “Trisomy” is a term that refers to a chromosomal condition where the body’s cells have a 3rd copy of a particular chromosome. Our DNA is packaged into chromosomes, which are small structures in each of our body’s cells. The usual number of chromosomes in each cell is 46, and the chromosomes come in pairs. So, each of our cells normally has 23 pairs of chromosomes.
Occasionally, and randomly, an egg cell or a sperm cell may donate an extra copy of a chromosome, for a total of 47 in the developing baby’s cells. These random occurrences could happen in any pregnancy; however, there is a slight increase in chance as the mother’s age increases. If the extra chromosome is #21, the condition that occurs is Down syndrome, or trisomy 21. Although any chromosome might be present in 3 copies, very few trisomies allow for a pregnancy to continue. Most trisomies result in early miscarriage.
Other trisomies that might allow a pregnancy to continue to full term are trisomy 13 and trisomy 18. These conditions are both much more rare than Down syndrome and both are very serious, causing poor growth of the baby, multiple birth defects, and very short lifespan. Pregnancies complicated by trisomy 13 or trisomy 18 may also miscarry or result in stillbirth.
A trisomy of the sex chromosomes is also possible. These conditions, known as XXX (a female with an extra X chromosome), XXY (a male with an extra X chromosome) and XYY (a male with an extra Y chromosome) are on the milder end of the spectrum for chromosomal disease. Usually any intellectual disability is mild compared to the other trisomies and lifespan is generally not shortened. There is no facial appearance to identify someone with a sex chromosome type of trisomy.
So, like many health conditions, trisomies can range from milder to more serious. The most important thing to know is that the vast majority of babies are born healthy and with the normal number of chromosomes!
Screening for certain trisomies is available to every pregnant woman and in most cases can be done early in pregnancy. If you have additional questions about trisomies, or any other genetic testing, our team of Genetic Counselors at Desert Perinatal Associates can help! They can answer questions about the conditions, screening and testing options for trisomies, and about local and national support organizations for trisomies.