Down Syndrome FAQ
What is Down Syndrome?
- Down syndrome individuals have spesific facial feature and have severe mental retardation. Many will also have heart and bowel conditions that require surgery. They are unable to attend normal school.
- It is the most common genetic (chromosomal) Condition discovered in babies where there is an extra chromosome 21 (trisomy 21).
How does Down Syndrome occur?
- Babies with Down syndrome have an extra chromosome-21.
- The affected ovum where failure of division of chromosome 21 occurred will have this extra chromosome 21.
- When it is united with a sperm the conception will have an extra chromosome 21, causing Down syndrome in the affected baby.
- The possibility of failure for chromosomes to divide in mothers’ ovum (egg) is a spontaneous phenomenon that increases with age of the mother.
- The average rate is 1 per 1000 pregnancies
The probability is closely related to the mother’s age with the chance increasing the older the mother. Every pregnancy has a chance. A 30 year old has a 1 in 550 chance. A 35 year old has a 1 in 270 chance.
There are no cases of Down Syndrome in my family. Can my baby get it?
- Most Down Syndrome is spontaneous and can happen in any pregnancy.
- See Question 2 above
What happens when a baby has Down Syndrome (clinical features)?
- Babies with Down syndrome have a characteristic appearance.
- 98% have major mental deficiencies and can only attend schools for special kids.
- Many have structural problems such as hole in the heart or blocked intestines that may require surgery after birth.
- They are almost always dependent on their parents or social welfare organizations for life. Very few are independent.
- There is no treatment available.
Why are there specialized tests to detect Down Syndrome in pregnancy?
- Down syndrome can appear normal on normal on detailed scans 30% of the time.
- Specialized screening tests increase their detection rate.
What screening tests are available for the detection of Down Syndrome in pregnancy?
- The 1st Trimester Detailed Genetic Scan done between 11 and 14th week of pregnancy (FTScan) has a 70% detection
- FT-Scan + risk calculation (accredited centres) has close to 90% detection (depends on protocol used by the sonographer – Aseana has a 90% detection rate on ultrasound alone)
- Combined blood+FTScan, cFTS, has a detection of 95%
- Fetal DNA tests (maternal blood), known as NIPT, has a detection of 99.99%
These tests carry no risks to baby.
Can the 2nd trimester Detailed Structural Scan detect babies with Down Syndrome?
- 30-40% of Down Syndrome are detected at the “Detailed Scan” at 20 weeks (2nd trimester)
- The detection rate of Down Syndrome is not as high as other specific screening tests described in Q5.
Why is the Triple Test or the Double Test not listed?
- These tests have a lower detection rate than ultrasound alone in the 1st trimester Detailed Genetic Scan (FTScan).
- These tests are rarely offered these days unless earlier options are missed.
Is there a diagnostic test (confirmatory)?
- Yes. Fetal or placental cells are sampled by amniocentesis or placenta biopsy (chorionic villous sampling, CVS) and sent for confirmatory genetic testing.
- The invasive procedures however carry a miscarriage risk of 0.5 to 1%
What is the best approach? Which test should I do?
- Start with the 1st Trimester Detailed Genetic Scan, FTScan, for a baseline genetic assessment as there are many other conditions too. If an abnormality on ultrasound is picked up other tests may be more relevant.
- If the FTScan is normal, consider further Down Syndrome testing as your budget would allow.
What are the possible results after I opt for a specific screening test?
- Tests typically report back as Low Risk or High Risk.
- A Low Risk result means the possibility of Down Syndrome is reduced significantly. But it could be falsely negative, ie baby has Down Syndrome but result flagged as Low Risk – this is uncommon.
- A High Risk result means that the possibility of Down Syndrome is significantly increased. But there is still a possibility of a false positive, ie baby is actually normal but results flagged as High Risk – this is uncommon.
Does a Low Risk result confirm the baby does not have Down Syndrome?
No. See Question 8
Does a High Risk result mean my baby has Down Syndrome?
- No. See Question 8
- There is still a possibility of baby being normal. Each test has its own false positive rate where normal babies are also flagged as High Risk.
- A diagnostic confirmatory test should be done after a High Risk result.