Genetic & chromosomal disorders
Screening and diagnostic tests
A number of tests are available that can help identify some of these conditions. Down syndrome, cystic fibrosis, fragile X, neural tube disorders such as spina bifida, and other inherited and chromosomal disorders can all be diagnosed with some level of certainty. However, no test is 100% correct every time.
As the baby develops, different tests can be used to pinpoint particular disorders. These tests can only be done at certain times during the pregnancy when the baby is at a particular stage of development.
There are two types of antenatal testing:
No test can guarantee a baby will be born healthy, so if you are considering having these tests, it is advisable to seek counselling as early as possible and to ask your doctor about the results and what they mean. You may be faced with having to make some difficult choices when considering the best course of action for you and your family. It can be an advantage having time to plan and prepare.
What we test for
1. Physical abnormalities such as neural tube defects of the skull (anencephaly) and spine (spina bifida).
2. Chromosomal abnormalities, of which Down syndrome is the most common. This condition results from an extra copy of chromosome 21.
3. Genetic disorders. Many inherited conditions can be tested for, including cystic fibrosis, fragile X, spinal muscular atrophy, haemophilia and thalassaemia. These tests are usually only performed on an amniotic fluid or placental sample if clinically indicated e.g. family history or parental gene carrier status.
Screening takes the form of blood tests and ultrasound. These are minimally invasive and can often be performed in the early weeks. However, screening is limited in what it can tell us. It cannot confirm a disorder, only assess the chance. Screening is best regarded as an indicator about whether more invasive diagnostic tests should be performed to provide further evidence.
Diagnostic testing involves passing a needle into the womb to take samples of amniotic fluid or tissue from the placenta. This procedure carries a small risk of infection and/or miscarriage. You will need to decide whether you are prepared to accept these risks, and how you will react if the test results are positive.