What is Down Syndrome?

Down Syndrome is the most common cause of learning difficulties in newborn babies.  It occurs in 1 out of every 700 babies.  Anyone can have a baby with Down Syndrome, regardless of age, family history or ethnic background.  However, a woman's risk of having a baby with Down Syndrome increases with age.

Down Syndrome is caused by having an extra copy of a particular chromosome (the part of cells that contain genetic material from our parents).

Individuals with Down Syndrome will have some degree of learning difficulty.  They are also at greater risk of having some medical problems, including heart defects, abnormalities of the digestive system, hearing and eyesight problems, seizures, thyroid problems and childhood leukaemia.  Life expectancy is around 40 to 60 years. 

The severity of the condition varies from person to person.  Prenatal testing can tell if a baby has Down Syndrome.  However, it is not able to predict how severely an individual will be affected.

What happens during the 11-14 weeks scan?

A moderately-filled bladder is generally preferred before the scan.

The length of the fetus would be measured.  It must measure between 45 to 84 mm for any risk estimation to be valid.  If the length of the fetus is less than 45 mm, a repeat scan will rescheduled.  If the length is more than 84 mm, an alternative method of screening for Down Syndrome will be discussed with you.

The nuchal translucency (NT) is measured at the back of the baby's neck.  If the measurement taken is larger than expected, this means that there is an increased risk that the baby could have Down Syndrome or other chromosomal abnormality.  However, most babies with a large NT measurement are born without Down Syndrome.

The computer software will use your date of birth and your gestational date (how many weeks pregnant you are) to calculate your age-related risk.  This is then combined with the NT measurement to calculate the overall risk of Down Syndrome.

Is detection of nasal bone useful?

Research has shown that two-thirds of fetuses with Down Syndrome and only 1% of fetuses with normal chromosomes have absent nasal bone on the 11-14 week ultrasound scan.  Hence the presence of nasal bone on ultrasound scan in reassuring.  The presence of a nasal bone would further reduce the risk of Down Syndrome, while its absence would further increase that risk.  If the nasal bone is absent, we suggest that a re-scan at 16 weeks be arranged to re-check and to measure the nasal bone if this is present.

How should I interpret the results of the Down Syndrome screening test?

As these tests are screening tests, the results will be given to you and your partner in the form of an estimated risk, based on the best available current scientific data.

For example, if you are informed that your baby's risk of Down Syndrome is 1 in 100, it means that among 100 similar pregnancies with the same measurement of the nuchal translucency, one pregnancy will eventually result in the birth of a baby with Down Syndrome.

What other tests are available?

If you are at increased risk (usually more than 1 in 300) of having a child with Down Syndrome, you will be offered another diagnostic test such as chorionic villus sampling or amniocentesis.  This test will give you a definite diagnosis of Down Syndrome or other major chromosome abnormalities.  However these tests carry a small risk (about 1%) of a miscarriage. 

What happens if Down Syndrome is diagnosed in my baby?

Although some medical complications resulting from Down Syndrome can be treated, there is no available specific treatment for any chromosomal abnormality.  Some patients carrying Down Syndrome fetuses may choose to carry on while others may choose to abort. 

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