Haemophilia and muscular dystrophy - types of Down syndrome tests

Haemophilia and muscular dystrophy: Some disorders, such as haemophilia and muscular dystrophy, are only found in boys (although girls may carry the disorder in their chromosomes and pass it on to their sons). Tell your midwife or doctor if these or other genetic disorders run in your family, as it may then be important to know your baby’s gender.

Down’s syndrome and genetic disorders tests

These tests are offered to all pregnant women. There are different ways of carrying out screening.

Combined screening for Down syndrome

Combined screening involves a blood test and an ultrasound scan. All women should have dating and nuchal translucency scans between eight and 14 weeks. These scans may be combined. The blood test measures two pregnancy-associated blood chemicals. At the scan, the radiographer measures the thickness of the nuchal translucency at the back of your baby’s neck. This measure is used to calculate your individual statistical chance of having a baby with Down’s syndrome.

This nuchal translucency scan can be used in multiple pregnancies.

Serum screening for Down syndrome  

Serum screening is a blood test that screens for Down’s syndrome, usually at about 16 weeks into your pregnancy. It measures three or four pregnancy-associated blood chemicals to give your individual statistical chance of having a baby with Down’s syndrome. Serum screening on its own is not recommended for twin and other multiple pregnancies.

Down syndrome screening results

Some maternity services give the result as ‘lower risk/screen negative’ or ‘higher risk/screen positive’.

If the screening test shows the risk of the baby having Down’s syndrome is lower than the recommended national cut-off, this is known as having a ‘low-risk’ result. A low-risk result means that you are at a low-risk of having a baby with Down’s syndrome, but it does not mean there is no risk.

If the result shows the risk of the baby having Down’s syndrome is greater than the recommended national cut-off, this is known as an ‘increased risk’ or ‘higher risk’ result. An increased risk means you will be offered diagnostic test but it does not mean that your baby definitely has the condition. The diagnostic procedure you will be offered is either chorionic villus sampling (CVS) or amniocentesis to give you a definite answer about Down’s syndrome. Your midwife or doctor will explain the result to you and help you decided whether you want to have further tests.