Our Services Pre-Natal Diagnosis Screening for Down's Syndrome

First trimester screening for chromosomal anomalies
What is OSCAR?
One Stop Clinic for Assessment of Risk for Down’s syndrome (OSCAR) is a screening method performed at 11-14 weeks of gestation. The following parameters are obtained to calculate the risks of having a Down’s baby for each individual woman:

• the woman’s age
• her serum level of pregnancy-associated plasma pr otein-A (PAPP-A)
• her serum level of free beta human chorionic gonadotr ophin (free-beta hCG)
• thickness of the baby’s neck-fold (nuchal translucency thickness)

What does it mean if the test result shows “increased risk”?
An “increased risk” or “positive” result does not mean that the baby is necessarily affected by Down’s syndrome. It merely indicates that further confirmatory tests need to be considered. After doctor assessment, you may consider to have non-invasive analysis of fetal DNA (SafeT21) or confirmatory invasive test. The confirmatory tests include, chorionic villous sampling (to be performed between 11-14 weeks of gestation) or amniocentesis (to be performed at 16-20 weeks of gestation). These tests help to confirm or refute the diagnosis of Down’s syndrome.

What does it mean if the test result shows “low risk”?
A “low risk” or “negative” result means the chance of a Down’s baby is low. If the pregnant woman accepts such low risk, there is no need for invasive prenatal diagnosis procedure, such as chorionic villous sampling or amniocentesis. However, it is also important to point out that OSCAR remains a screening test. A result showing “low risk” cannot completely exclude the possibility of having a baby with Down’s syndrome or other chromosomal anomalies

Advantages of OSCAR

• High detection rate (90%);
• Ultrasound examination is safe to the baby;
• Suitable for women of any age;
• It can be performed in early gestation and hence there is plenty of time to make decision should the results be positive;
• If the baby is conrmed to be affected, there is still enough time to consider all management options;
• If a termination of pregnancy is chosen for an abnormal baby, it carries less risks to the women when performed in early gestation.

Non-invasive Fetal DNA testing (safe T21)

• safeT21 is a non-invasive prenatal DNA test developed for the screening of fetal chromosomal abnormalities, such as Down syndrome, Edwards syndrome (trisomy 18) and Patau syndrome (trisomy 13). During pregnancy, the unborn child releases some of its DNA into the blood circulation of its mother. safeT21express^TM is a test that measures the amount of DNA molecules from chromosomes 21, 18, 13 and others in the blood samples of pregnant women
• An abnormally increased amount of chromosome 21 DNA molecules in a pregnant woman’s blood sample is suggestive of Down syndrome (the sensitivity is 99.65% with false-positive rate of 0.03%)
• An abnormally increased amounts of chromosome 18 DNA molecules in the pregnant woman’s blood sample is suggestive Trisomy 18 (the sensitivity is 99.9% with false-positive rate of 0.01%.)
• An abnormally increased amounts of chromosome 13 DNA molecules in the pregnant woman’s blood sample is suggestive trisomy 13 (the sensitivity is 99.9% with false-positive rate of 0.02%)
• Additional chromosomal abnormalities may be able to detected, including sex chromosomal abnormalities (eg 45 XO, 47 XXY, 47 XXX and 47 XYY) and some common microdeletion problems (eg. 1p36 deletion syndrome, 2q33.1 deletion syndrome, 22q11 deletion syndrome (include DiGeorge syndrome), Angelman syndrome, Cri-Du-Chat syndrome, Langer-Giedion syndrome and Prader–Willi syndrome
• The accuracy of the safeT21express^TM test as described above is based on the requirement of the tested baby contributing adequate amounts of DNA into the maternal plasma sample.

What procedures are involved in this test?

• An ultrasound examination to measure the size of the fetus and determinate the gestation
• Blood taking from pregnant women for assessment

What does it mean if the test result shows “positive”?
A “positive” result does not 100% confirm that the baby is affected with chromosomal abnormality. There is a chance of false positive result. So, positive test results should be confirmed by amniocentesis or chorionic villus sampling.

What does it mean if the test result shows” negative”?
A “negative“ result means the chance of baby affected with Down ‘s syndrome, trisomy 18, trisomy 13, sex chromosomal abnormalities and common microdeletion syndrome is very low. However, it is also important to point out that safe T21 remains a screening test. It cannot completely exclude the possibility of having baby with these chromosome abnormalities. So Invasive testing (eg. amniocentesis or chorionic villus sampling) may sometime be necessary to confirm the diagnosis.

Second trimester screening for Down's syndrome (Quadruple Test)
It is a noninvasive screening test for Down syndrome with a detection rate of around 83% and false positive rate of 5%. The test is carried out between 16-19+6 weeks pregnancy using biochemical markers (alpha fetal protein AFP, unconjugated estriol uE3, free beta human chorionic gonadotrophin b-HCG, Inhibin A) and maternal age for risk calculation.