Why is the Imagining Futures project also looking at screening for Down's Syndrome?
As part of the Imagining Futures project, the attitudes of families living with Spinal Muscular Atrophy (SMA) towards SMA screening will be compared with their attitudes to screening for other conditions. Specifically, attitudes towards the existing programme for Down's Syndrome screening. This is to explore whether people who have experience with one condition are more or less likely to be in support of screening for another, contrasting condition. A dataset exploring the views of 993 pregnant women undergoing screening for Down's Syndrome will be compared with the views of families living with SMA to see if there are differences in how these two groups view screening for Down's Syndrome- when one group has experience of living with a genetic condition in their family and the other hasn't.
Down's Syndrome has a very different presentation to SMA, although like SMA, there is a wide range of severities. Down's Syndrome is caused by an extra copy of chromosome 21 which leads to some degree of learning difficulty, although there is a wide variation in the extent and impact of that learning difficulty. Similarly, Down's Syndrome is known to be associated with particular health problems, including heart problems, reduced vision and hearing as well as early-onset Alzheimer's Disease (a form of senile Dementia). However, Down's Syndrome varies from person to person and many people living with condition are in very good health. The life expectancy for people with Down's Syndrome is between 50 and 70 years (NHS Screening Programmes, 2012).
All pregant women in the UK, regardless of age, are offered antenatal screening for Down's Syndrome. The most common method of screening for Down's Syndrome is called the 'combined test' which involves a blood test and a scan.
The blood test
Unlike genetic screening for SMA, blood test screening for Down's Syndrome looks for certain proteins and hormones in the mother's blood rather than at particular genes. It it carried out between 10 and 14 weeks of pregnancy.
At around 12 weeks of pregnancy, an ultrasound scan is offered which is used to measure the amount of fluid lying under the skin at the back of the baby's neck. This is called the nuchal translucency (NT) measurement.
The combined screening result
A computer programme then takes the results of the blood test combined with the ultrasound results (as well as information about the mother's weight age, week of pregnancy, family origin and smoking status) to produce a risk figure (NHS Screening Programmes, 2012).
Women who are deemed to have a higher chance of having a baby with Down's Syndrome, either due to their age or their screening test result, will be offered a diagnostic test. This diagnostic test is done using either chorionic villus sampling (CVS) or amniocentesis. These tests involve taking a small sample of either the placenta (CVS) or amniotic fluid (amniocentesis) to look at the baby's chromosomes. Down's Syndrome can usually be diagnosed by these tests. As is the case for SMA, there are no effective treatments or a cure for Down's Syndrome that can be offered either in utero or after birth (although many of the health problems associated with Down's Syndrome such as heart problems, may be treated), so women and couples who are given a prenatal diagnosis of Down's Syndrome (or SMA) must make a decision to either continue with the pregnancy or else have a termination.
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