Tests to find abnormalities or chromosomal conditions
When pregnant you may be offered tests that can find structural abnormalities. These include spina bifida, which is a defect in the development of the spine, or some chromosomal conditions like Down’s syndrome, which is caused by having an extra chromosome. You can discuss these tests with your midwife.
Screening tests can:
- reassure you that your baby has no detected structural abnormalities
- give you an opportunity to see your baby during the scan
- give you time to prepare for the individual needs of your baby
Tests can also give you valuable information for your care during the pregnancy.
However, no test can guarantee that your baby will be born without an abnormality. No test is 100 per cent accurate and some abnormalities may stay undetected.
If you do have a screening test and it suggests an increased chance of a genetic condition, you will be offered diagnostic tests, which will give a more definite diagnosis.
These diagnostic tests carry a small risk of miscarriage, so you may decide not to have them.
Talking to your partner, midwife, doctor and friends about the issues may help you decide what is right for you.
You may also be offered tests for:
- sickle cell
- glucose tolerance test
Screening for Down’s syndrome, Edwards' syndrome, and Patau's syndrome
During the very early stages of development changes can take place leading to some babies having an extra chromosome, causing Down’s syndrome, Edwards’ syndrome, or Patau’s syndrome.
If you would like to find out if your baby has an increased chance of having one of these syndromes you should ask your midwife or doctor about the quadruple test or the Harmony test.
These are private tests which need to be self-funded, but can be carried out in some Trusts and is done by taking a sample of your blood after 14 weeks of pregnancy for the quadruple test or after 10 to 12 weeks for the Harmony test.
The quadruple test is mainly used to predict the chance of your baby having Down’s syndrome by measuring the level of certain biochemical markers within your blood sample.
The Harmony test analyses fragments of the baby’s DNA found in your blood sample to predict the probability of your baby having one of the above syndromes.
These type of tests are called non-invasive or cell-free DNA tests.
Following a higher chance result you will be offered referral to the Fetal Medicine Assessment Unit (FMAU) in Belfast for a more detailed scan and further diagnostic tests will be offered such as an amniocentesis.
The diagnostic tests can give you valuable information for your care during pregnancy and for the care of your baby after delivery.
However, no test is 100 per cent accurate and not all syndromes are tested for, so some conditions or syndromes may stay undetected.
Amniocentesis can be offered from 15 weeks of pregnancy if:
- you have a positive or higher chance quadruple test screening result
- an ultrasound scan detects an abnormality that is associated with a genetic condition
- your past history or family history suggests that there may be an increased chance of your baby having a genetic or chromosomal condition such as Down’s syndrome, sickle cell disease, or thalassaemia
Using ultrasound as a guide, a fine needle is passed through the wall of the abdomen into the amniotic fluid that surrounds your baby.
Within the fluid are cells that contain the same chromosomes as your baby. A small sample of this fluid is drawn off and sent to a laboratory for testing.
Most women feel only mild discomfort.
Usually, the fluid will be tested for Down’s syndrome, Edwards’ syndrome, and Patau’s syndrome.
The results should be available within three working days. If all the chromosomes have to be looked at, it can take up to three weeks.
This test will reveal your baby’s sex, so tell your midwife or doctor whether, at this stage, you want to know if your baby is a boy or a girl.
Amniocentesis has a 0.5 to one per cent risk of miscarriage. At most, one test in 100 will result in pregnancy loss.
When deciding whether to go ahead with this test, try to balance the risk of miscarriage against the value of the result to you.
Diagnostic tests for Down's syndrome and other genetic conditions
These tests will give you a definite diagnosis of Down’s syndrome and other conditions.
Your midwife or doctor will explain what is involved and you will usually be offered counselling.
If a test confirms your baby has a genetic condition
It is always difficult when you are told your baby has a condition.
Your midwife or doctor will make sure you see the appropriate health professionals to help you get all the information and support you need so you can make the choices that are right for you and your family.