27/11/2013 12:41 GMT | Updated 22/05/2015 10:12 BST

Q: What Is The Quadruple Test?

The quadruple test is a blood test taken from a pregnant woman to screen for the possibility of Down's syndrome and spina bifida.

It is named the quadruple test as it measures the level of four particular substances in a woman's blood. These comprise AFP, beta HCG, Inhibin-A and Oestriol.

This information is combined with the woman's age, weight, and the age of the pregnancy to determine her individual risk factor.

Because it is a serum screening test, as opposed to a genetic test, it cannot provide a definitive diagnosis. Instead, it determines the woman's risk of carrying a baby that has either one of these conditions. Currently, the test can identify 75 of babies with spina bifida.

While the test is completely safe and presents no risk to the baby, it can only be performed between week 15 and week 22 plus six days of pregnancy. For this reason, it cannot be performed until a dating scan has been done, which is normally at around 12 weeks of pregnancy.

Additionally, if the woman is pregnant with twins or other multiple pregnancy, the accuracy of the scan decreases. The test cannot be performed on an insulin-dependent diabetic.

If the serum screening test reveals that a woman's risk is high for either of these conditions, further tests are available. These include amniocentesis or chorionic villus sampling, both of which will provide a pinpoint diagnosis.

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