Down Syndrome causes mental retardation and learning disability in children.
Down Syndrome is the most common cause of significant mental retardation and learning disability in children.
It is caused by a change in chromosomal number (genetic makeup) in the egg before it is fertilised by the sperm (at the time of conception). This usually occurs due to chance, and is more common in older mothers.
As a result, the fertilised embryo contains an extra chromosome 21 making it three instead of the usual pair (hence the name trisomy 21).
It is important to know that people with Down Syndrome can also have reasonably long and fulfilling lives.
Throughout the world, the frequency of Down Syndrome is about one per 700 births.
The risk of having a baby with Down Syndrome increases as the mother’s age increases (refer to Table 11.1).
Until recently, the only factor used to identify women at high risk for Down Syndrome was their age.
At age 35, for example, the chance of having a baby with Down Syndrome is about one in 250. This has led to many hospitals offering
amniocentesis to women over a certain age, usually 35 or 37.
There are several other methods available to pick up Down Syndrome. These tests are grouped into screening and diagnostic tests.
Screening tests do not tell you if your baby has Down Syndrome. Their purpose is to tell you if your foetus belongs to a low or high risk group.
If the screening test shows that there is a high risk of your baby being affected, you will be offered a diagnostic test (see below) to confirm it.
Screening tests are noninvasive; hence, there is no risk of miscarriage to the baby.
A result of one in 300 means that 299 out of 300 women with this particular test result will not have an affected baby, and only one will. As you can see, it is not a test for the presence of a Down Syndrome baby, but a way of comparing your chance of having one. So, a 40-year-old woman would be very reassured by a result of one in 800 and a 20-year-old woman may opt for amniocentesis if her result was one in 100 (Figure 11.3).
Overall, about six to seven out of 10 Down Syndrome babies will be detected by the serum screening. However, there will still be some that are undetected and will be born to mothers who have had a “low-risk” result.
These screening tests do not guarantee that the baby will be healthy. It only helps to screen for Down Syndrome. If the test result is “low risk”, this means that the chance of having this condition is reduced.
It must be clearly understood that the results of screening tests represent risks. Increased risk does not mean that the baby is affected and further diagnostic tests must be done.
A low risk does not exclude the possibility of Down Syndrome or other abnormalities as the risk assessment does not detect all affected pregnancies.
These are tests that obtain cell samples from the baby and can tell you for sure if the baby is affected with Down Syndrome. It is only performed for high-risk cases detected on screening due to the inherent risks of miscarriage associated with these procedures.
The purpose of diagnosing this condition is to allow the couple the various options of whether to continue with the pregnancy or have an abortion.
After the amniocentesis or CVS, it is important to return to the hospital immediately if you run a fever, experience any unusual lower abdominal pain,
vaginal bleeding or leakage of fluid from the vagina.
Source: Dr TAN Thiam Chye, Dr TAN Kim Teng, Dr TAN Heng Hao, Dr TEE Chee Seng John, The New Art and Science of Pregnancy and Childbirth, World Scientific 2008.
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This article was last reviewed on
22 Nov 2023
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