What is Down syndrome?
Down syndrome is a chromosomal condition caused by extra genetic material. Typically, our cells contain 23 pairs of chromosomes. In the case of Down syndrome, a person has an extra full or partial copy of chromosome 21. This extra genetic material changes how the body and brain develop. People with Down syndrome have a few common physical traits, but each individual is unique and can lead a healthy active life.
We don’t know for sure why Down syndrome happens. Even though it’s a genetic condition, the majority of the cases are not passed on from the parents or family to the baby. Most cases happen because in the early stages of the baby’s development, there is a problem when the cells are dividing. However, there are some factors that may increase the risk of having a baby with Down syndrome, such as:
- Mother’s age. The risk of Down syndrome increases with the mom’s age. Even though the risk is greater as your age increases, about 80 percent of babies with Down syndrome are born to women age 35 or less. This is because younger women have more babies than older women.
- Having had a baby with Down syndrome. Up to age 40, for each pregnancy your chances of having another baby with Down syndrome is about 1 in 100 (1 percent). After age 40, the risk is based on your age. Talk to a genetic counselor to understand your risk of having another baby with Down syndrome.
- Being a carrier of a genetic translocation. Both, men and women, can pass a genetic translocation to their baby. These cases are not very common. If you had a baby with Down syndrome before or if you or your partner have a family history of Down syndrome, it’s best to talk to a genetic counselor.
During pregnancy your health care provider will offer screening tests to see if your baby is more likely to have Down syndrome. These tests are offered to all pregnant women as part of regular prenatal care. However, a screening test won’t tell you for sure if your baby has Down syndrome. It only tells you if there is a higher risk. To know for sure you will need a diagnostic test.
How do you know if your baby has Down syndrome?
If you get an abnormal screening test result, your provider will recommend a diagnostic test. A diagnostic test will confirm if a baby has Down syndrome. There are few diagnostic tests:
- Amniocentesis (also called amnio). This test checks the amniotic fluid surrounding your baby in the uterus to check for Down syndrome. You can get an amnio at 15 to 20 weeks of pregnancy.
- Chorionic villus sampling (also called CVS). This test checks the tissue from the placenta to see if a baby has Down syndrome. You can get a CVS at 10 to 13 weeks of pregnancy.
- Cordocentesis (also called percutaneous umbilical cord sampling or PUBS). For this test your provider inserts a thin needle into an umbilical cord vein to take a small sample of your baby’s blood to check for chromosome defects. You can get this test between 18 and 22 weeks of pregnancy. There’s a much greater risk of miscarriage with cordocentesis than with an amnio or a CVS. So you only get this test if other tests are unclear and your provider can’t confirm if your baby has Down syndrome any other way.
Down syndrome is also identified at birth by physical traits like: almond-shaped eyes that slant up, low muscle tone, a single line across the center of the palm of the hand, and a flattened face. But these traits won’t tell you for sure if your baby has Down syndrome, a chromosomal test call karyotype is needed to confirm this diagnosis.