What is a combined test?Show [+]Hide [-]
This is a screening test performed in two parts. Both parts must be completed for a result to be given:
The first part is an ultrasound scan which dates the pregnancy and measures the skin thickness at the back of the baby’s neck (the Nuchal Translucency or NT).
The second part is a blood test taken from you after the scan where the levels of two substances (proteins) in your blood are measured. When combined with the NT measurement in the laboratory these results provide the risk of your baby having Down’s syndrome.
Will this test tell me if my baby has Down’s syndrome or not? Show [+]Hide [-]
There are tests which will give definite information. These are called diagnostic tests. Diagnostic tests increase the risk of miscarriage which is why we do not offer diagnostic tests to all women. Instead, we offer all women a Combined Test (CT) which carries no risk of miscarriage. This type of test is called a screening test. Screening tests do not give a definite answer, but they do tell us which babies have an increased risk of having Down’s syndrome. We then offer diagnostic tests to the women at increased risk.
- For every 100 Combined Tests we perform, we will find two women who have a high risk for Down’s syndrome.
- Because the combined test is a screening test, it will not place every woman, who actually has a baby with Down’s syndrome, into the high risk group. It will, however, correctly place nine out of 10 (90%) of these women into the high risk group.
What is a high risk result?Show [+]Hide [-]
A high risk result is more than one chance in 150 of the baby having Down’s syndrome. For example, one in 50.
Being high risk does not mean the baby definitely has Down’s syndrome.
If you have a high risk result you will be contacted by a specialist midwife (usually by telephone) within three working days and offered further counselling to help you decide whether you want to have a diagnostic test or not.
When will the result be available? Show [+]Hide [-]
A low risk result – you will receive a letter sent out to your home address by post. You should receive this within two weeks of the Combined Test appointment.
A high-risk result – you will be contacted within three working days of your appointment for the Combined Test.
When can the Combined Test be performed? Show [+]Hide [-]
The tests can only be performed between 11 and 13 weeks and six days of the pregnancy. If you are outside this range we will discuss the options available to you which will include taking a blood test from you later in pregnancy.
What else does the scan look for?Show [+]Hide [-]
The scan will show the early development of the baby. This will identify some but not all major abnormalities (four out of 10 or 40% of abnormalities will be seen). You will still need your 20 week scan when more details will be seen. If you have any questions about this please ask the sonographer performing your scan who will be happy to answer your queries.