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Testing for Down Syndrome During Pregnancy

Testing for Down Syndrome During Pregnancy

Testing for Down Syndrome During Pregnancy

What is Down Syndrome?

Down syndrome is a condition caused by an additional chromosome, which can lead to physical and mental impairment. Children with Down syndrome may have a delay in intellectual development, as well as heart, hearing and visual defects.

Risk Factors for Mothers

While ethnicity does not seem to be a factor — globally, around 1 in every 800 births produces a Down syndrome baby, among women of every race — age is. Older mothers are more at risk. A woman’s chances of giving birth to a child with Down syndrome are higher if she is aged 35 and older.

Testing for Down Syndrome

Down syndrome cannot be prevented, but you can detect it early on in the pregnancy. In fact, as Dr Tan Thiam Chye, an obstetrician and gynaecologist says, it is often covered at your first check-up during pregnancy.

There are a few different methods of testing, but a popular method is the OSCAR test, which stands for One-stop Clinic for Assessment of Risk for Foetal Anomalies. Usually recommended around 12 weeks into the pregnancy, OSCAR uses a sonogram (also known as an ultrasound) to scan the neck thickness and nose bone of the developing baby. Doctors will also take a small blood sample from the mother, which they will analyse. “The accuracy of [the OSCAR] test is about 90%,” says Dr Tan.

However, there are a range of tests to choose from, which vary in their methods, accuracy and cost. There is also a genetic blood test which detects foetal cells, so discuss the pros and cons with your doctor.

If preliminary screening tests find that you are at higher risk of giving birth to a baby with Down syndrome, there are confirmatory tests available. However, these tests are more invasive. One such test is chorionic villus sampling, which involves a biopsy of the placenta. While this test has the advantage of also being able to test for other genetic issues, it carries a miscarriage risk of approximately 1%.

Another test: an amniocentesis, also involves an ultrasound scan and sampling. During the scan, doctors will insert a needle into the amniotic sac to draw out some amniotic fluid for testing. This also carries a small miscarriage risk of between 0.5% and 1%.

Your Baby, Your Choice

The important thing to remember is that there are a range of testing options for you to explore if you think you are at risk of having a baby with Down syndrome. If you like, you can also choose not to have these tests done — they are completely optional.

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A/Prof Tan Thiam Chye
MBBS (S'pore), M.Med(O&G) (S'pore) Head & Senior Consultant Department of Obstetrics and Gynaecology KK Women's and Children's Hospital Director (Clinical), Office of Patient Experience Deputy Director (Education), KKH Campus Associate Professor Duke - NUS Graduate Medical School Singapore

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