What is Down syndrome?
Down syndrome occurs at the time of conception and is not under the direct influence of a woman or her partner. When someone has Down syndrome, there is an extra copy of the 21st chromosome in their cells and they have 47 chromosomes instead of 46. Therefore, another name for Down syndrome is trisomy 21.
Down syndrome is the most common chromosome disorder that we know of. Statistically, 1 in 1,100 babies born worldwide will have Down syndrome.
People with Down syndrome have a range of characteristics which vary between individuals. Intellectual, developmental and health challenges are common, as is having certain characteristic physical features.
When can I get tested for Down syndrome?
Risk factors for Down syndrome
- Advancing maternal age is one clear risk factor for having a baby with Down syndrome. This is because older eggs do not divide as well as younger ones do. After the age of 35, the risk increases. However, most Down syndrome babies are born to women under the age of 35 because women in this category have more babies.
- Being carriers for genetic translocation for Down syndrome can be passed on by both men and women.
- Having one child with Down syndrome previously.
Combined first trimester screening
A computer analysis combines the results of the two tests and the mother's age to give a risk profile of the baby having Down syndrome. If there is found to be an increased risk, a diagnostic test may be advised.
Non-invasive prenatal testing (NIPT)
Down syndrome and other chromosomal abnormalities are tested for in the NIPT. If the result shows an increased likelihood of the baby having Down syndrome, diagnostic testing such as chorionic villus sampling (CVS sampling) and or amniocentesis are recommended.
Different screening tests can provide different results. Sometimes results can indicate a high chance of Down syndrome when the baby does not have it. A low chance result can also be returned when it is present.
Ask your maternity care provider about the specific testing you are being offered.
Second trimester screening
Most pregnant women have an ultrasound between weeks 18 and 20 of pregnancy. This helps to see that the baby is growing and developing normally. It is also to screen for any complications. Down syndrome may be detected at this scan.
Diagnostic tests for Down syndrome
Diagnostic tests for Down syndrome increase the chances of miscarriage, so they need to be carefully considered before giving consent. Women who have had previous children with genetic or chromosomal abnormities and older women are more likely to be advised to have diagnostic testing.
Chorionic villus sampling and amniocentesis
Chorionic villus sampling is also known as CVS. This is when a fine needle is used to collect cells from the placenta. Laboratory testing looks for missing, abnormal, or extra chromosomes which show Down syndrome is likely. CVS is generally done between weeks 11 and 14 of pregnancy.
Amniocentesis is a test where a fine needle collects a small amount of amniotic fluid. It is examined to look for extra or missing chromosomes. Amniocentesis is generally done between weeks 15 and 18 of pregnancy. An ultrasound is done at the same time to minimize risk and make sure the needle is inserted accurately.
Both CVS and amniocentesis involve collecting a sample of the baby's genetic material to be examined in a genetics laboratory. Results from tests are generally back within a week.
Diagnosing Down syndrome after birth
Things to consider
Frequently asked questions about Down syndrome testing
You will need to speak with your maternity care provider about the results. Depending on the findings, you may be referred to a genetic counselor.
Do I have to have testing for having a baby with Down syndrome?
Like all other prenatal tests, you have a choice about what screening is right for you.
The information of this article has been reviewed by nursing experts of the Association of Women’s Health, Obstetric, & Neonatal Nurses (AWHONN). The content should not substitute medical advice from your personal healthcare provider. Please consult your healthcare provider for recommendations/diagnosis or treatment. For more advice from AWHONN nurses, visit Healthy Mom&Baby at health4mom.org.