First Trimester Screening for Down Syndrome

What is Down syndrome?

The majority of pregnancies are normal but in some cases, the baby is born with a chromosomal abnormality. Down syndrome is a set of mental and physical symptoms that result from an extra copy of chromosome 21 (3 copies of chromosome 21 instead of 2 copies in a normal child).
Although children with Down syndrome may have some physical and mental features in common, symptoms of Down syndrome can range from mild to severe. Children with Down syndrome are slower in mental and physical development. 30-40% of individuals with Down syndrome are born with heart defects. 8-12% of them have problems with their intestines when they were born. Children with Down syndrome may have problems with their ears, eyes, thyroid and skeleton. They are also at higher risk of having blood cancers (leaukaemia)
In Malaysia, the incidence of Down syndrome is one in every 660 births. The chance of having a baby with Down syndrome increases as a woman gets older. However, it is important to note that 80% of babies with Down syndrome are born to women under 35 years of age. Down syndrome cannot be cured but many individuals with Down syndrome live productive lives well into adulthood.
Mother’s Age (years)
Risk of Down syndrome
Risk of all Chromosomal Abnormality
1 in 1667
1 in 526
1 in 1429
1 in 500
1 in 1250
1 in 476
1 in 1176
1 in 476
1 in 1053
1 in 435
1 in 952
1 in 384
1 in 769
1 in 323
1 in 500
1 in 238
1 in 385
1 in 192
1 in 294
1 in 156
1 in 227
1 in 127
1 in 175
1 in 102
1 in 137
1 in 83
1 in 106
1 in 66
1 in 82
1 in 53
1 in 64
1 in 42
1 in 50
1 in 33
1 in 38
1 in 26
1 in 30
1 in 21
1 in 23
1 in 16
1 in 18
1 in 13
1 in 14
1 in 10
1 in 11
1 in 8
Table 1. Data showing the risk of Down syndrome and all chromosomal abnormalities relating to the age of the mother
2. How can I know whether my baby have Down syndrome?
There are some tests you could perform to check whether your baby has Down syndrome. The confirmatory test is to perform an invasive test such as chorionic villous sampling or amniocentesis, which check the baby for he/her chromosomal make-up. However, these tests carry risks of miscarriage, infections and complications such as pre-labour preterm rupture of the water bag (please refer to our articles on chorionic villous sampling and amniocentensis).
Recent studies have shown that ultrasound measurement of the nuchal transluscency (thickness of the fluid behind the baby’s neck) and absence of nasal bone will detect almost 90% of Down syndrome. This test is usually carried out between 11 weeks to 13 weeks and 6 days gestation. The detection rate can be increased by combining the test with serum screening which is done by taking your blood and measuring the level of two hormones (beta- hCG & PAPP-A) in your body. These tests are called the screening tests for Down syndrome.
The screening test for Down syndrome gives you an estimation of the risk of your baby having Down syndrome and does not tell you whether your baby has Down syndrome or not. However, it can help you to decide whether you want to undergo confirmatory testing by chorionic villous sampling or amniocentesis. A low risk result means that your baby has low risk of having Down syndrome but it doesn’t mean that there is no risk at all. A high risk result (if your result shows that your risk is between 1 in 2 chance to 1 in 249 chance) means that you have a higher than average chance of having a baby with Down syndrome, but it doesn’t mean your baby definitely has the condition.
Picture 1 : An ultrasound scan showing the Nuchal Translucency measurements being done
Picture 2: An ultrasound showing the nasal bone measurements being done
3. How long would the result take?
You should receive your result within a few days.
4. Is the test safe?
This test is non-invasive and involves having an ultrasound scan and taking some blood from you. Therefore, it does not harm your baby and is safe.
5. What are the limitations of the test?
Again, this test is a screening test and not a confirmatory test. It does not tell you exactly whether your baby is having Down syndrome or not. The test is expensive and may not be widely available in all medical centres and laboratories. The measurement of nuchal transluscency requires expertise (obstetricians or ultrasonographers) who is trained and certified in performing this test, which may not be widely available in some places.
The majority of pregnancy with chromosomal abnormalities ended with miscarriage. Therefore, there had been constant debate whether performing a first trimester screening is cost-effective compared to second trimester screening (triple test) for Down syndrome.
6. What are the advantages of this test compared to second trimester screening/ triple test for Down syndrome?
 The first trimester screening test is done during the first trimester and is more sensitive than the second trimester screening test. It allows early detection of Down syndrome and subsequent management of the pregnancy.
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(1)   National Health Service (UK) patient information:
(2)   Hook EB, Cross PK, Schreinemachers DM. Chromosomal abnormality rates at amniocentesis and in liveborn infants. Journal of the American Medical association. 1983; 249: 2034-2038.
(3)   Kiwanis Down Syndrome Foundation, Malaysia:
(4)   Persatuan Sindrom Down Malaysia:
(5)   Luesley DM, Baker PN. Obstetrics & Gynaecology, an evidence-based text for MRCOG. First edition. 2004. Arnold Publishers. London.

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