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Prevention of Down's syndrome
Screening
All pregnant women, whatever their age, should be offered screening before 20 weeks. These tests are all optional.
The triple test is performed after 14 weeks of pregnancy but before 20 weeks. The best time for the most accurate results is between 16-18 weeks. It is a blood test that tests for the hormone Human Chorionic Gonadotrophin (hCG), the protein alpha-feto (AFP ) and the protein unconjugated oestriol (uE3 ).
Low levels of AFP, low levels of uE3 or high levels of hCG in the blood may mean a higher than average risk of having a baby with Down’s Syndrome.
The results of the blood test are combined with the mother’s age to estimate the risk of Down’s Syndrome. The results will be either screen negative (risk is less than 1 in 250) or screen positive (risk is more than 1 in 250). A screen positive test result does not mean that there is an abnormality. It only means that there is an increased risk and further tests may be needed to be more accurate.
Results are not 100% accurate. At the moment, less than 5 in 100 people have a false-positive result (at least 60 out of 100 cases of Down’s Syndrome are detected). By April 2007, this false-positive rate should be less than 3 in 100 (more than 75 out of 100 cases of Down’s Syndrome will be detected).
The quadruple test is similar to the triple test but also tests inhibin A. This is only used if you are at a very high risk of having a baby with Down’s Syndrome.
The nuchal translucency scan (taken between 10 and 13 weeks of pregnancy) is only available in certain hospitals. It involves measuring the width of the baby’s spinal cord.
Diagnostic tests
An amniocentesis test involves taking a sample of the amniotic fluid that surrounds the unborn baby. It is carried out with local anaesthetic using a thin needle to remove the amniotic fluid. This contains some of the baby’s cells and can be used to try and diagnose Down’s Syndrome. Results take 3-4 weeks. There is a 1 in 200 chance of miscarriage with this test.
A chorionic villous sampling (CVS) test involves taking a sample of tissue from the placenta to measure certain markers in the blood. It is carried out under local anaesthetic using a thin needle passed into the wall of the abdomen or by inserting a small tube through the vagina and the cervix (neck of the womb) to remove some of the chorionic villi (placental tissues). Results take 10-14 days. There is a 1 in 100 chance of miscarriage with this test.
Decisions
Although results are not 100% accurate, it can be a worrying and difficult time if your diagnostic tests indicate a high risk of having a baby with Down’s syndrome. You will be encouraged to have some counselling and to discuss the results with a doctor, nurse or midwife and your partner. There are a number of options available to parents who are expecting a baby with Down’s Syndrome.
Research into a cure
Research is being carried out on chromosome 21 to better understand the development of people with Down’s Syndrome and why there is a higher incidence of certain medical complications in people with the condition.
