What is a Quad Test?
A Quad Test is based on an ultrasound dated second trimester blood sample. Four biochemical markers are used to determine the risk for Down Syndrome (AFP, B-hCG, Oestriol and Inhibin).
Why would a pregnant woman have a Quad Test?
All women are at risk of having a baby with chromosomal problems like Down's Syndrome. Although the risk increases with age, it can happen to anyone.
Some pregnant women will choose to have a screening test to see what their personal risk is for having a baby with Down's Syndrome and if the risk is high enough they may choose to have a diagnostic test like an amniocentesis to see if their baby definitely does or does not have Down's Syndrome.
What does the Quad Test involve?
A sample of your blood is taken at around 15 or 16 weeks of pregnancy (between 14 and 23 weeks is acceptable). The stage of pregnancy is best estimated by an ultrasound dating scan. The concentration of four substances in your blood will be measured. The four markers are: alpha-fetoprotein (AFP) free ß-human chorionic gonadotrophin (free ß-hCG) unconjugated oestriol (uE3 ) inhibin-A (inhibin)
In pregnancies with Down's Syndrome, AFP and uE3 levels tend to be low and free ß-hCG and inhibin levels tend to be raised. The level of AFP is also used to determine if there is an increased risk of spina bifida or anencephaly.
Can any other abnormalities be identified?
Yes, the Quadruple test also indentifies pregnancies at a high risk of Edward's Syndrome (trisomy 18). The risk of Edward's Syndrome can be identified using AFP, uE3 and free ß-hCG.
What is defined as a screen-positive result?
Down's Syndrome: If the risk of having a term pregnancy affected with Down's Syndrome is 1 in 150 or higher the result will be screen-positive and you will be offered an amniocentesis. If the risk is lower than 1 in 150 the result will be screen-negative and an amniocentesis will not be recommended.
Open neural tube defects: If the AFP level is two and a half times the average level or higher, the result will be screen-positive and a detailed ultrasound scan will be offered.
Edwards' Syndrome: If the risk of having a term pregnancy affected with Edwards' Syndrome is 1 in 150 or higher you are offered an ultrasound examination and amniocentesis.