Screening for three genetic conditions: Down’s syndrome, Edwards’ syndrome and Patau’s syndrome, are currently offered to all pregnant women. Which tests women are offered depends on how far along their pregnancy is. Women between 10 and 14 weeks pregnant are offered a blood test plus an ultrasound scan, called the combined test, while women between 14 and 20 weeks of pregnancy are offered a different blood test , which is less accurate than the combined test.
If you test positive, your doctor will then recommend you undergo diagnostic testing, specifically chorionic villus sampling (removing and testing a small sample of cells from the placenta) or amniocentesis, when a needle is used to extract a sample of amniotic fluid, the fluid that surrounds the foetus in the womb.
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The risks
The combined prenatal test has its drawbacks. It has a false positive rate (when a foetus is diagnosed with a problem, but is in fact healthy) of around three to four percent. What this means is that many women have unnecessary, invasive diagnostic tests that come with around a one in 100 chance of causing a miscarriage. What is needed is a prenatal test that reduces the false positive rate of the screening test. This would reduce the number of women with healthy babies who need invasive testing.
A better method?
A new technique promises to reduce the false positive rate of prenatal screenings. The Harmony Prenatal Test works by analysing the fragments of foetal DNA contained in the mother’s blood to predict the risk of certain genetic conditions. All that’s needed is a maternal blood sample taken at week 10 of pregnancy or later, which is then submitted to a laboratory. Results can be received within seven days.
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The benefits
The Harmony Test gives a much lower false-positive result compared to traditional screening techniques. Published studies have shown that the test results in a 0.1 percent false-positive rate for Trisomies 21, 18 and 13 (Down’s, Edwards’ and Patau’s syndrome) which is lower than the three to four percent rate in traditional screening tests. It is important to remember, however, that if you do test positive you will still need to undergo diagnostic tests.
Did you know….
Chromosomes are packages of DNA that contain the information we need to grow and develop. Normally, people have 23 pairs of chromosomes. But in genetic conditions like Down’s, Edwards’ and Patau’s syndrome there is an extra copy of a chromosome. Usually this happens by chance and isn’t inherited from the parents, which is why all pregnant women are offered screening. The Harmony Test measures the number of chromosomes in the mother’s blood to see if there are any of these extra chromosomes
Screening during pregnancy
It’s routine to be offered screening tests during pregnancy to try to find any health problems that could affect you or your baby, not just to test for genetic conditions like Down’s syndrome but also for infectious disease and physical abnormalities. These tests can help you then make choices about care while you’re pregnant and after the birth.
The tests offered during pregnancy are either blood tests or ultrasounds, or a combination of both. Ultrasounds can detect physical abnormalities like spina bifida, while blood tests can find the risk for inherited disorders such as sickle sell anaemia. Combined tests can be used for detecting chromosomal abnormalities, like Down’s syndrome. It’s important to remember that screening tests typically don’t say for certain if you or your baby have a health problem, it just tells you whether you or your baby have a high or low risk of having a problem. A diagnostic prenatal test is usually needed to give a definite ‘yes’ or ‘no’ answer. It’s also entirely up to you whether you choose to have a screening test.
For more information on the Harmony Test, visit ariosadx.com
See also: What to Expect When you’re Expecting
