Also in Scanning and Ultrasound:
You choose whether or not to have the screening test. It is a personal choice for you and your partner to make. All pregnant women irrespective of age can have the test.
The CUB (Combined Ultrasound and Biochemical) screening test is carried out between 11 and 14 weeks of pregnancy. Depending on the results of this test some women (about 1 in 20) will be offered a second follow up test.
For the screening test an ultrasound measurement of the fluid-filled area at the back of the baby's neck is taken. This is called Nuchal Translucency (NT).
A small blood sample is also taken from your arm and is sent to the laboratory where levels of two naturally occuring factors called Free beta HCG and PAPP-A are measured. Within 1 week of having this test you should receive a telephone call letting you know whether you are low risk or higher risk for Down's syndrome.
If the screening test is low risk there is only a very small chance that your baby will have Down's syndrome and for most women no further testing is required. 19 out of 20 women will be low risk.
No. The screening test can identify about 85% Down's syndrome pregnancies. Occasionally other types of abnomality are found.
If the screening results are "high risk", this indicates that the NT measurement combined with the biochemical measurements and your age show that there is an increased chance that the baby has Down's syndrome and a further, follow-up test will be offered. You will be asked to return to the department where the results will be discussed with you, your questions answered, and the type of follow-up tests explained.
It is important to note that a high risk screening result does not indicate with certainty that there is an abnormality, and that most women with these results will have normal, healthy babies. Follow-up tests such as CVS or amniocentesis are offered to check whether the baby has Down's syndrome.
Follow-up tests are used where the screening result indicates that further investigation of the pregnancy should be considered. They include:
CVS (chronic villus sampling): This follow-up test is offered up to 15 weeks of pregnancy. A fine needle is inserted through the abdominal wall into the placenta and a tiny piece of placenta is removed. This is sent to the laboratory and used to examine the developing baby's chromosomes. The result of the CVS test takes about 2 weeks and will show whether the baby has Down's syndrome or normal chromosomes. There is a lower than 1 in 50 chance of miscarriage following CVS.
Amniocentesis: This follow-up test is offered from 15 weeks of pregnancy. A needle is inserted through the abdominal wall into the fluid (called amniotic fluid) surrounding the baby. A small amount of fluid is removed and sent to the laboratory where it is used to examine the baby's chromosomes. The result of the Down's syndrome test takes about 5 days and a complete examination of the baby's chromosomes takes up to 3 weeks. There is a 1 in 200 chance of miscarriage following amniocentesis.
Ultrasound (also known as "scanning"): Depending on the results of the screening test, a few women may be invited to have a further scan later in pregnancy around 20 weeks. This is to allow a more detailed examination of the baby when it is larger in size.
In most cases follow-up testing finds a perfectly healthy baby. If Down's syndrome is found this will be discussed fully with you and your partner and help and advice will be available to help you decide what to do. Some couples may decide to continue with the pregnancy while others may feel that termination of the pregnancy is their preferred choice. There is no pressure from the hospital staff to influence your decision, only help and support.
Further information on the CUB screening test can be obtained when you go for your scan. You can also email the Scanning Department if you have any particular queries regarding this test.