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Down syndrome occurs when a baby is born with an extra chromosome 21, leading to intellectual disability and congenital heart disease. The older the woman, the more likely she is to have a Down's baby. Doctors would recommend that pregnant women be screened for Down syndrome. The following is a comparison of Down syndrome tests:
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Method
|
Test name and method
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Weeks
|
Detection rate of Sown syndrome
|
Specimens
|
Pros and cons
|
|
Non-invasive
|
1. First trimester screening (Investigation of the zona pellucida by ultrasound + maternal blood sampling)
|
11-13 weeks
|
90-91%
(Plus measurement of fetal nasal bone)
|
Maternal serum
|
Pros: Ultrasound including early fetal structural examination.
Cons: Ultrasound technology has a high threshold and requires additional exam time, and the detection rate is limited.
|
|
Non-invasive
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2. Second trimester screening
(Four indicators for maternal serum Down syndrome screening )
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15-20 weeks
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81 %
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Maternal serum
|
Pros: Only maternal blood is needed, and the threshold for testing is low.
Cons: The detection rate is low as the examination weeks are late.
|
|
Non-invasive
|
3. Noninvasive prenatal fetal chromosome testing
(Maternal blood is drawn to test fetal chromosomes)
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10 weeks or more
|
99 %
|
Maternal-fetal chromosomes
|
Pros: The testing of Down's syndrome, Edwards syndrome (T18) and Patau syndrome (T13) is accurate and safe.
Cons: It is expensive and the testing items are limited.
|
|
Invasive (amniotic fluid extraction)
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4. Amniocentesis
(Fetal cells are cultured in amniotic fluid drawn for fetal chromosome analysis)
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16-20 weeks
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> 99 %
|
Chromosomes
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Pros: Techniques for diagnosis, with the addition of array CGH, are the most complete examination of chromosomes
Cons: The chance of miscarriage is about 1-3/ 1000 for an invasive amniotic cavity examination
|
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