What are the screening tests for these conditions?
Your antenatal team will offer you the screening tests for Down’s, Edwards’ and Patau’s syndromes, but it is your decision whether to have the test or not. Some people want to screen while other people prefer not to. Everyone has different beliefs and it’s important to think carefully about what the results will mean for you if you decide to have the test.
A screening test isn’t the same as a diagnostic test. It’s important to understand the difference so you can choose whether or not you want to have the tests. A screening test aims to identify if your baby is at high risk of one of these three chromosomal abnormalities. If this test is positive, you will be offered a diagnostic test. This is a test that can say for definite whether or not your baby has one of these conditions.
There are three screening tests for Down’s, Edwards’ and Patau’s syndromes.
- The combined test is a blood test which looks at the levels of two blood markers (Papp-A and HCG) combined with an ultrasound test that measures the thickness of the nuchal pad (a pocket of fluid) at the back of the baby’s neck. This test is done between 11 and 13 weeks of pregnancy.
This test aims to work out the risk of your baby having Down’s, Edwards’ or Patau’s syndrome. You can choose to screen for any one or all three of these conditions. Depending on the results, your doctor may advise you to have the quadruple test before considering having a diagnostic test.
- The quadruple test is a blood test that screens for Down’s syndrome. It looks at the levels of four blood markers (AFP, beta HCG, inhibin-A and oestriol). The test measures the levels of these markers to indicate if there’s a high risk of your baby having Down’s syndrome. The test is usually done between 15 and 20 weeks.
If the results show that there is a high risk, your doctor will have a conversation with you about what this means before you consider going on to have a diagnostic test.
- The DNA test is a blood test that screens for Down’s syndrome. It analyses DNA fragments in your blood (this is called cell-free DNA). The test aims to find out if there is more chromosome 21 in the DNA than is normal. Examples of this test include Harmony, Verfi, Panorma Test, and Maternity21P offered by private clinics. The NHS does not routinely offer the DNA test at the moment (unlike the combined test and the quadruple test). Research is still being carried out to decide whether to make the DNA test available or not.
The results of the DNA test give you an indication of the risk of your baby having Down’s syndrome. If the results are positive (your baby is at high risk), your doctor will explain more about what this means and answer any questions you have. You might then consider whether or not to have a diagnostic test.
It’s important to remember that screening tests can’t tell you whether or not your baby has Down’s, Edwards’ or Patau’s syndrome. A low-risk result doesn’t mean your baby doesn’t have an abnormality; equally, a high-risk result doesn’t mean that your baby does. That’s why, if you choose, you can go on to have a diagnostic test.