When a women is pregnant, some of the baby’s DNA floats around freely in the mother’s blood stream. By taking a blood sample of the mother’s blood, we are able to detect and analyse the baby’s DNA and screen the pregnancy to see if there is any chance for Down syndrome, trisomy 18 or trisomy 13.
NIPT is performed from a single tube of the mother’s blood from 10 weeks of pregnancy. The results from NIPT are much more accurate than other traditional screening tests, and the detection rate for chromosomal defects is much higher.
NIPT is safe for the mother and the pregnancy, with no associated risk for miscarriage.
Because NIPT is a screening test, any abnormal results will have to be confirmed with CVS (chorionic villus sampling) or amniocentesis. Your doctor will advise which is most appropriate for you.
Cell-free DNA
Chromosomes are thread-like structures in the nucleus of our cells that contain our DNA. We usually have 46 chromosomes arranged in 23 pairs. The first 22 pairs are numbered 1-22.
The last pair is the pair of sex chromosomes:
It is essential that each of our cells contains the right number and configuration of chromosomes.
1 tube of the mother’s blood is drawn as early as 10 weeks of gestation.
You will receive the result within 10 working days of the blood being drawn
Your results will tell your doctor whether or not trisomies 21, 18, 13 or sex chromosome abnormalities (if ordered) are highly likely to be present in your pregnancy. In the case of a positive result, your healthcare provider will discuss what the results mean and what the next steps are.
Your test report will include 3 possible results for chromosomes 21, 18 and 13:
If sex chromosome option is ordered, results will be reported as either No Aneuploidy detected or Aneuploidy detected.
Screening tests – screening tests can be a blood test, ultrasound or a combination of both to estimate the chance for certain birth defects. It is important to remember that a screening test does not provide a definitive answer about the condition that is being tested. If a screening test shows that there is a chance for a certain defect, a diagnostic test must be performed.
Diagnostic tests – diagnostic tests analyse DNA in detail from a sample of the pregnancy.
The two most common diagnostic tests available to pregnant women are chorionic villus sampling (usually called CVS) and amniocentesis.
CVS can be performed by a specialist between weeks 10–14 of pregnancy. In this procedure, a small sample of the placenta is removed either by inserting a small needle through the pregnant woman’s abdomen or by inserting a tube (called a catheter) through the cervix.
Amniocentesis can be performed in the second trimester of pregnancy or later. During amniocentesis, a small needle is inserted through a pregnant woman’s abdomen, and a small amount of the fluid is removed from the amniotic sac.
After either procedure, the sample is sent to a laboratory where the chromosomes are analysed.
Additional testing for other conditions can be performed on the sample from the CVS or amniocentesis, if indicated based on your specific family or medical history.
With both of these procedures, there is a risk of complications, including a small risk for miscarriage.
A false positive result indicates that the given condition is present when it is not, i.e. the test result will show that there is a chromosomal abnormality when in fact there is not.
A false negative results indicates that the given condition is not present when it actually is, i.e. a chromosomal abnormality does exist but it does not show on the test.
There is a small chance that false positive or false negative tests results can occur. This is normal in any screening test. If there is any doubt, a diagnostic test must be done to confirm or exclude a diagnosis (the presence of an abnormality).
If the TriScreen test comes back positive i.e. a defect has been reported in one of the chromosomes, you will need to have a diagnostic test like CVS or amniocentesis. Your doctor will advise which is most appropriate.
If the TriScreen test comes back negative i.e. all the chromosomes are normal, and the ultrasounds look normal, then you will not need a CVS or amniocentesis.
The TriScreen test can test for the sex of the baby. This test is OPTIONAL. If you do not want to know the sex of the baby, you will not be told the outcome of this part of the test.
Sex chromosome testing can only be done in singleton pregnancies. It cannot be done in twin or triplet pregnancies.
If your healthcare provider chooses, the TriScreen prenatal test can also be used to identify:
The about expanded aneuploidy and microdeletion tests must be requested separately. If any abnormality is found, the test must be confirmed with a CVS or amniocentesis.
The TriScreen test is a highly accurate advanced screening test. However, no test can guarantee a baby will have no medical issues. The TriScreen test only addresses aneuploidies of chromosome 21, 18, 13 and the sex chromosomes, if ordered. It does not test for, or report, all genetic and non-genetic problems that may occur in your unborn child. If the test result is No Aneuploidy Detected, indicating a negative result, it does not completely rule out all potential problems with chromosome 21, 18, 13 or all sex chromosome aneuploidies in your baby.
Genetic counselling before and after testing is recommended.
Results of Aneuploidy Detected or Aneuploidy Suspected are considered positive and women who receive such results should be offered diagnostic tests, such as CVS or amniocentesis, for confirmation.