Quad Test (Wolfson) 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). The blood samples are sent to: W Huttley, Antenatal Screening Co-ordinator, Wolfson Institute of Preventative Medicine, St Bartholomews Royal School of Medicine Dentistry, Charterhouse Square, LONDON EC1M 6BQ (FAX: 020 7882 6290, TEL: 020 7882 6293). For further information see www.smd.qmul.ac.uk/wolfson/epm/screening.

What does the Quadruple test involve?
A sample of your blood is taken at around 15 or 16 weeks of pregnancy (between 14 and 22 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 250 or higher the result will be screen-positive and you will be offered an amniocentesis. If the risk is lower than 1 in 250 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 100 or higher you are offered an ultrasound examination and amniocentesis.

Performance of the Quadruple test using a 1 in 250 at term cut-off

Down's syndrome:
Detection Rate (DR): 84% 84% of women with pregnancies affected with Down's syndrome will receive a screen-positive result. (The remaining 16% of women with pregnancies affected with Down's syndrome will receive a screen-negative result.)

False Positive Rate (FPR): 5.0% 5.0% of women whose pregnancies are not affected with Down's syndrome will receive a screen-positive result. (95% of women whose pregnancies are not affected with Down's syndrome will receive a screen-negative result.)

Odds of being affected given a positive result (OAPR): 1:23 Among women in the screen-positive group, 1 woman will have a pregnancy with Down's syndrome for every 23 who do not.

Open neural tube defects
Detection Rate (DR): 85% for open spina bifida; nearly all cases of anencephaly are detected.

False Positive Rate (FPR): 1%

Edwards' syndrome:
Detection Rate (DR): 60%

False Positive Rate: 0.1%