There are different kinds of prenatal genetic screens: The earlier you see your health care provider, the more options you will have.
The following table shows the different screening options available based on how far along you are in your pregnancy: What do the prenatal screening results mean? A prenatal screen result tells you the chance of your baby having Down syndrome, trisomy 18, or an open neural tube defect. How is my result calculated? The levels of proteins made by the baby and the placenta are measured in your blood.
If you have a nuchal translucency ultrasound, the amount of fluid normally found at the back of the baby's neck is measured. A baby with Down syndrome, trisomy 18 or an open neural tube defect may have different amounts of these proteins or fluid. These differences are used to estimate the chances for your pregnancy.
Other factors that affect the results include the dating of your pregnancy, your age, weight, ethnic origin and whether it is a twin pregnancy. As part of your screen result, you will be given a number that estimates the chance your baby has one of these conditions. This number is compared to the screen cut-off. The screen cut-off is the chance above which you will be offered diagnostic testing.
If your chance is lower than the screen cut-off, this is called a screen negative result. If this number is higher than the screen cut-off, this is called a screen positive result. What does a screen negative result mean? If your result is screen negative, the chance that the baby has Down syndrome, trisomy 18 or an open neural tube defect is low.
You can be more than What does a screen positive result mean? If your result is screen positive it does not mean that your baby has the condition. In fact, most women with this result do not have a baby with one of these conditions. Diagnostic testing tells you for sure if your baby has any of these three conditions.
What if my result is screen positive for Down syndrome or trisomy 18? If your result is screen positive for Down syndrome or trisomy 18, your health care provider may need to confirm how far along you are in your pregnancy. Amniocentesis will tell you if your baby has either of these conditions. NIPT will give you a new risk very low or very high to have a baby with Down syndrome or trisomy If your risk is found to be very high on NIPT, an amniocentesis would then be needed to confirm.
It is your choice whether you have the amniocentesis or not. What if my result is screen positive for an open neural tube defect? If your baby does have an open neural tube defect this will usually be seen on the ultrasound scan. My result is screen positive. A Screen Positive Result: You have learned that the result of your prenatal genetic screen is "screen positive. As part of your screen result, you have been given a number that estimates the chance your baby has one of these conditions.
For example, the chance of Down syndrome is 1: This is the same as saying: Your health care provider may need to confirm how far along you are in your pregnancy. It is important to make sure the pregnancy dating used for the prenatal screen result is correct. If your baby has an open neural tube defect, this is usually seen on the ultrasound scan. What is an amniocentesis? It is a diagnostic test. It tells you for sure if your baby has Down syndrome or trisomy It is done by putting a very fine needle into your belly to remove a few teaspoons of amniotic fluid from around the baby.
The needle is guided by ultrasound so it does not touch the baby. The baby's cells that are in the fluid sample are looked at to find out whether your baby does or does not have Down syndrome or trisomy 18 or another chromosome condition. If a rapid lab test is done that looks only at chromosomes 13, 18, 21 and the sex chromosomes, results are available in three days. If all chromosomes are analyzed, results are available in two weeks.
In other words, if women have an amniocentesis, one would lose the pregnancy as a result of the procedure. What is non-invasive prenatal testing NIPT? It is a safe and highly accurate screening test for Down syndrome and trisomy 18 that is done through a blood test. It detects almost all babies with Down syndrome and trisomy This means that if the test is negative, the chance of Down syndrome or trisomy 18 is extremely small.
If the test is positive, the chance is high. An amniocentesis would then be offered to confirm the result. The NIPT test result is available in days.
This test is covered by the provincial medical plan for women who meet one of the following criteria: Visit our NIPT page for more information. My prenatal screen result is screen positive for Down syndrome or trisomy 18? Should I have extra testing? It is your choice. Think about these questions to help make up your mind. Do I think the chance that is given on my screen result is high or low? Do I need to know for sure if my baby has Down syndrome or trisomy 18 before the baby is born? If I find out that my baby has Down syndrome or trisomy 18, what will I do with this information?
Will I end the pregnancy? Will I continue the pregnancy? Will I make an adoption plan for the baby? Most women who have the amniocentesis do not lose their pregnancy, but do I think the 1 in chance of pregnancy loss is too high for me to take? Will I feel too worried for the rest of my pregnancy if I do not have more follow-up testing such as the amniocentesis or NIPT?
What if I am having trouble deciding whether having an amniocentesis is right for me? Both medical genetics programs offer face-to-face and telehealth counselling. Telephone counselling could be done if telehealth is not available.
The decision to refer for genetic counselling should be a joint decision between you and your health care provider. What if the result of the amniocentesis show that the baby has one of these conditions? How is diagnostic testing different from screening?
Diagnostic testing tells you for sure whether or not your baby has one of the conditions being screened for. Screening tells you the chance that your baby has one of the conditions to help you decide whether or not to have diagnostic testing.
What diagnostic tests are available? A few teaspoons of the fluid surrounding the baby amniotic fluid is taken out through the needle. The needle is guided by ultrasound, so that it does not touch the baby. The amniotic fluid contains skin cells from the baby. Testing can be done on these cells to accurately determine if the baby has Down syndrome, trisomy 18, trisomy 13, or an abnormal number of the sex chromosomes. Amniocentesis can tell you for sure whether or not the baby has Down syndrome or trisomy However, amniocentesis is associated with a one in risk of miscarriage.
Amniocentesis is usually performed after 15 weeks of pregnancy. The needle is used to collect a small piece of the placenta, known as the chorionic villus.
The needle is guided by ultrasound so that it does not touch the baby. The sample contains cells from the baby. As with amniocentesis, CVS can tell you for sure whether or not the baby has Down syndrome or trisomy However, there is a one in chance of miscarriage from the CVS procedure. CVS is done between weeks of pregnancy. If a rapid lab test is done that looks only at chromosomes 13, 18, 21, and the sex chromosomes, results are available in three days.
There are times when the rapid lab test does not give conclusive results. In such cases, the full analysis is required with results available around two weeks after the procedure. Detailed Ultrasound In a detailed ultrasound examination, a specialist looks carefully at every part of the baby to ensure the baby is growing and developing as expected.
The ultrasound can tell whether the baby has an open neural tube defect. It can also confirm how far along you are in the pregnancy, and whether twins are present. Unlike amniocentesis or CVS, detailed ultrasound has no risk of miscarriage.