The Trisomy 21 Prenatal Screening Program of Québec gives pregnant women and couples access to a screening test for Trisomy 21 if they want to be tested.
Trisomy 21, also known as Down syndrome, is caused by the presence of an extra chromosome in the 21st pair of the 23 pairs of chromosomes found in every cell in the human body. It is one of the most common chromosomal abnormalities. Trisomy 21 is not generally hereditary. Around 1 in 770 babies is born with Trisomy 21.
Every woman, no matter what her age, has a chance of having a child with Trisomy 21. However, the probability increases with the pregnant woman’s age, as shown in the following figure.
The figure below shows that the probability of having a child with Down syndrome varies with the woman’s age. At age 20, there is 1 case in 1528. At age 25, there is 1 case in 1351, while at age 30, there is 1 case in 909. At age 35, there is 1 case in 384 and at age 40, there is 1 case in 112. Lastly, at age 45, there is 1 case in 28.
People with Trisomy 21 have mild to severe intellectual disabilities. They may also have other health problems, such as heart and bowel malformations or epilepsy.
Most children with Trisomy 21 are able to talk and walk, but it takes them longer to learn to talk and walk and develop motor skills than other children. The treatment and support they are given at an early age influence their development.
People living with Trisomy 21 have the potential to develop deep emotional relationships and to lead lives that are fulfilling both for themselves and their loved ones. Most will need varying degrees of support throughout their life. Some people with Trisomy 21 have jobs and live almost completely independent lives.
All pregnant women can have a screening test for Trisomy 21, irrespective of their age. However, women with a multiple pregnancy, meaning women who are carrying more than one baby, are not eligible for the Program owing to the limitations of the screening test at present. Women who are pregnant with twins or triplets, for example, must speak to their doctor to find out about the various options available to them.
In Québec, the blood tests in the Program are offered free of charge to all women who have a health insurance card. There may, however, be a fee for nuchal translucency testing. Amniocentesis is also reimbursed by the Régie de l’assurance maladie du Québec.
At your first pregnancy visit, your doctor or midwife will talk to you about participating in the Trisomy 21 Prenatal Screening Program of Québec. The health professional will offer you a test to calculate your probability of having a child with Trisomy 21 and, if necessary, will suggest that you have amniocentesis in order to get a definitive diagnosis.
Test to calculate your probability
The blood test results combined with your age-related probability will be used to determine whether you are unlikely or very likely to give birth to a baby with Trisomy 21. There is no risk for the pregnancy if you have this test.
Screening involves taking 2 blood samples from the mother during pregnancy, and may or may not include nuchal translucency testing:
- A 1st blood sample is taken between week 10 and week 13
- A 2nd blood sample is taken between week 14 and week 16
Proteins and hormones from the baby or the placenta are measured in each blood sample. A single blood test can be done, but 2 will give a more reliable result.
Nuchal translucency testing
Between the 11th and the 13th weeks of pregnancy, your doctor or midwife might suggest that you have a dating ultrasound to check how far along you are in your pregnancy. When this ultrasound is done, the baby’s nuchal translucency may be measured. This is the space between the skin and the spine at the back of a baby’s neck. If this space appears larger than normal, the probability that the baby has Trisomy 21 is higher. Nuchal translucency testing, combined with the 2 blood tests, improves the reliability of the calculation of your probability of having a child with Trisomy 21.
Possible test results
The results of the blood tests and nuchal translucency testing will tell you if your probability of giving birth to a baby with Trisomy 21 is low or high:
- Low probability (result is less than 1 in 300): it is unlikely that your baby has Trisomy 21. You do not need to have other tests to confirm the result. However, this result does not guarantee that your baby does not have Trisomy 21. Given the natural differences between individuals and the limitations of prenatal screening, blood tests and nuchal translucency testing cannot detect all cases of Trisomy 21.
- High probability (result equal to or higher than 1 in 300): it is very likely that your baby has Trisomy 21, but this does not necessarily mean that it does. Your doctor or midwife will suggest that you have a diagnostic test, amniocentesis, to confirm for sure whether or not your baby has Trisomy 21.
If the baby has Trisomy 21, the parents must decide if they want to:
- Continue the pregnancy and prepare to be the parents of a child with Trisomy 21
- Continue the pregnancy and give their child up for adoption
- Terminate the pregnancy and cope with the resulting grief
Limitations of the test
- The results of the blood tests and nuchal translucency testing will not tell you for sure. They will only tell you the probability. A high probability result, for example, does not necessarily mean that your baby will have Trisomy 21. Only amniocentesis will tell you for sure whether or not your baby has Trisomy 21.
Amniocentesis is a diagnostic test that detects chromosomal abnormalities. A fine needle is inserted into the pregnant women’s abdomen to remove a sample of amniotic fluid. Since amniotic fluid contains fetal cells, amniocentesis allows the baby’s chromosomes to be analyzed. The test can be performed as of the 15th week of pregnancy.
Complications can occur after amniocentesis. For this reason, the test is offered only to pregnant women who have a high probability of having a child with Trisomy 21.
The amniocentesis results will tell you for sure:
- The baby does not have Trisomy 21
- The baby has Trisomy 21
Complications can occur after amniocentesis. The most common minor complications (2 to 5% of cases) are:
- Loss of a small amount of amniotic fluid
- Uterine contractions
- Abdominal pain
The major complication is miscarriage. The risk of miscarriage after amniocentesis is between 1 in 200 and 1 in 100, or between 0.5 and 1%.
Limitations of amniocentesis
- While amniocentesis may confirm that a baby has Trisomy 21, it does not provide specific information, for example, about the level of intellectual disability, the presence of physical defects or possible health problems.
- The amniocentesis result can cause anxiety about having to make a decision about continuing or terminating the pregnancy.
Participation in the Program is voluntary. It is a personal choice and is up to you. To help you make a decision, you can talk to your partner, your family and friends, the health professional you are seeing for your pregnancy, a genetics professional or groups of parents of children with Trisomy 21.
To help you in your reflection, you can ask yourself the following questions:
- Do I want to know my probability of having a baby with Trisomy 21?
- How will I react if the probability test result shows that the probability is high?
- Do I want to have amniocentesis to be sure, despite the risk of a miscarriage?
- Do I want to terminate my pregnancy if I find out that my baby has Trisomy 21 and then deal with my grief for my baby?
- Do I want to continue my pregnancy if I find out that my baby has Trisomy 21 and raise my child or, alternatively, give it up for adoption?
Remember that you are free to have the screening test or not, depending on your situation and what you want. The decision is personal and you will have your own reasons for your choice. You should also know that you can always refuse to have the amniocentesis test when the time comes or decide to withdraw from the Program at any time.
If you decide to have the screening test, your doctor or midwife will have you sign a consent form and will help you with the steps involved.
If you decide not to have the screening test, you will not have to sign anything. Your doctor or midwife will answer your questions and tell you how the pregnancy is progressing.
Help and support
Deciding whether or not to participate in the Trisomy 21 Prenatal Screening Program of Québec is not necessarily easy. Deciding to end or carry a pregnancy to term knowing that the baby has a chromosomal abnormality is even harder.
If the outcome of your participation in the Program means that you have to make a choice between continuing and ending your pregnancy, you may need help.
If necessary, your doctor or midwife can refer you to psychology services that will support you in your reflection. Do not hesitate to discuss this choice with your family and friends or with a health professional. You can also contact groups of parents of children with Trisomy 21; this might help you make the decision that is right for you.
To find out the contact information for groups in your area, ask the professional you are seeing for your pregnancy follow-up.
Last update: 07 May 2012, 17:11