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Screening tests

Screening tests are non-invasive tests that can be offered to all pregnant women. They are not diagnostic. Instead, they help to identify women where the chance of having a baby with Down's syndrome is greater than 1 in 250.

Risk / Chance

The terms "risk" and "chance" refer to the possibility of an event happening. For example, a risk of 1 in 100 means that out of 100 women with this result, 1 will have a baby with Down's syndrome and 99 will not. This is the same as a 1% chance that the baby has Down's syndrome and a 99% chance that the baby does not.

Screening results

Screen negative

With most screening tests, if the probability / statistical chance of having a baby with Down's syndrome is less than 1 in 250 (e.g. 1 in 300, 1 in 400), it is called "screen negative" and you would usually not be offered a diagnostic test such as an amniocentesis. Screen negative does not rule out the possibility that your baby might have Down's syndrome.

Screen positive

With most screening tests, if the probability / statistical chance of having a baby with Down's syndrome is greater than 1 in 250 (e.g. 1 in 200, 1 in 150), it is called "screen positive" and you will be in the recall group and will be offered a diagnostic test such as an amniocentesis. The diagnostic test is optional - the final decision whether or not to have the test is yours.

One hormone level in the blood serum screening test - the AFP level - is used to screen for neural tube defects such as spina bifida. If this level is higher than usual, you will be offered an ultrasound scan as a diagnostic test.

Other Test Information

Some facts

Screening for Down's syndrome:

Around 1 in every 20 women who have a blood serum screening test at 16 weeks for Down's syndrome will come back in the recall group.
Of these 1 in 20 women, around 1 in 60 will have a baby with Down's syndrome.
Of these 1 in 20 women, around 59 out of 60 will not have a baby with Down's syndrome.

Screening for neural tube defects:

Around 1 in 40 women who have a blood serum screening test at 16 weeks will come back in the recall group for a neural tube defect.
Of these 1 in 40 women, around 1 in 20 will have a baby with a neural tube defect.
Of these 1 in 40 women, around 19 out of 20 will not have a baby with a neural tube defect.