Risks and prenatal testing for Down's syndrome
For every 1,000 babies born, one will have Down's syndrome. About 1,000 babies are born in the UK with Down's syndrome each year. The condition occurs in families from all social, economic, cultural, religious and racial backgrounds. Accurate figures for the number of people with Down's syndrome in the country, or in different regions, are not available. It is only in the past few years that the number of babies born with Down's syndrome has been accurately recorded.
The chance of having a baby with Down's syndrome increases with maternal age. The risks are calculated as follows:
25 years old: one in 1,400
30 years old: one in 800
35 years old: one in 380
38 years old: one in 190
40 years old: one in 110
45 years old: one in 30
The majority of babies with Down's syndrome are born to younger women, since the overall birth rate is higher in younger women.
The chance that parents of one child with Down's syndrome will have a second child with the condition can be greater than that of the general population. Genetic counselling is therefore very important.
It is possible to find out if a pregnant woman is carrying a child with Down's syndrome. The most commonly used diagnostic test is called an amniocentesis. This is usually carried out in the fourth month of pregnancy and involves taking a sample of the fluid surrounding the baby in the womb. It is almost 100% accurate in detecting Down's syndrome, but carries a risk of miscarriage of around one in 100.
Screening tests are also available. These do not state categorically whether or not the unborn child has Down's syndrome; instead, they give an estimated chance of the baby having the condition.
One such test is the Triple test. This involves a blood sample being taken from the mother in the fourth month of pregnancy.
Some hospitals offer an ultrasound screening test called Nuchal Translucency or Nuchal Fold. The test is carried out between 11 and 13 weeks from the date of the last menstrual period (LMP). The ultrasound measures an area that appears as a black stripe down the back of the foetus. A combination of measuring the nuchal fold and the mother’s age will give a statistical probability about the possibility of Down Syndrome or other chromosomal abnormalities.
It is vital that counselling is given in conjunction with all prenatal testing.
The Down’s Syndrome Association and the parents it represents do not believe that having a baby with the condition is a reason to terminate a pregnancy. However, it acknowledges that this is a decision for individuals to make.
For further information please contact
The Down’s syndrome Association
155 Mitcham Road
London, SW17 9PG
Tel: 020 8682 4001
Fax: 020 8682 4012 Visit their web site at www.dsa-uk.com