Quad Screen Test - Prenatal Genetic Screening
The quad screen — also known as the quadruple marker test, the second trimester screen or simply the quad test The quad screen is a test done in the second trimester to check for some birth defects.
The quadruple test for Down’s syndrome uses your age and the levels of four substances measured:
- Beta-human chorionic gonadotrophin (made by the placenta)
- Unconjugated estriol (made by the placenta and baby’s liver)
- Alpha-fetoprotein (made by the baby)
- Inhibin A (made by the placenta)
WHEN IS THE QUADRUPLE TEST OFFERED AND DO I HAVE TO TAKE IT?
The combined screening test is offered to women between 11 and 14 weeks. If you book too late for the combined test you will be offered the quadruple test.
Also if your baby is lying in a position where the fluid at the back of the neck cannot be measured (the nuchal translucency scan) the combined test will not have been possible. In this situation you will be offered the quadruple test.
You don’t have to have the test—that decision is yours. Some parents would rather know the chances of their baby being affected by a condition so that they can prepare for future decisions, whereas others don’t want to know.
WHAT ARE THE RISKS?
Because it’s a screening test and not invasive, the test is safe—there’s no risk of miscarriage or other pregnancy complications. Waiting for test results can be an anxious time though.
IS IT ACCURATE?
The quadruple test is recognised as slightly less accurate than the combined test but will identify around 80 of 100 babies who have Down’s syndrome.
HOW TO INTERPRET THE RESULTS
Your quadruple test results won’t tell you for certain if your baby does or doesn’t have Down’s syndrome, instead they will give you the chance—either higher chance or lower chance—that you might be carrying a baby with this condition.
You may get your results as a set of numbers that use a cut-off point of 150 for a higher chance result.
- Higher chance: if your result is 1 in 150 or 1 out of a number less than 150 (e.g. 1 in 100) then your baby has a higher chance of having Down’s syndrome.
- Lower chance: if your result is more than the cut-off value of 150 (e.g. 1 in 200) then your baby has a lower chance of having Down’s syndrome.
HOW IS THE TEST DONE?
The quadruple test is performed with a simple blood test. The health professional taking your blood will insert a needle into your arm and take a sample that will be sent to a laboratory for analysis.
Time taken to receive your results can vary depending on where you live. Your midwife will tell you when you should expect to hear your results.
Why it's done
- Down syndrome (trisomy 21)
- Trisomy 18
- Spina bifida
- Abdominal wall defects
