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The serum integrated test

The Serum Integrated test is an option for women who are unable to have a nuchal translucency measurement performed.

This page explains:

What does the Serum Integrated test involve?

The Serum Integrated test is performed in two stages. The first stage is ideally performed at 11 weeks of pregnancy, but any time between 10 and 13 weeks of pregnancy is acceptable. The second stage is ideally performed at 15 or 16 weeks, but between 14 and 22 weeks is acceptable.

The first stage involves:

  1. Taking a sample of your blood to measure the concentration of pregnancy associated plasma protein-A (PAPP-A).
  2. Providing you with a recommended date for taking a second blood sample for the second stage of the test.

The second stage involves:

  1. Taking a blood sample to measure the concentration of the following four markers:
    • alpha-fetoprotein (AFP)
    • total human chorionic gonadotrophin (hCG)
    • unconjugated oestriol (uE3)
    • inhibin-A (inhibin)
  2. Integrating the measurements from the first and second stages into a single screening result. The levels of the five markers in your blood are used, together with your age, to estimate your risk of a Down’s syndrome pregnancy.

In pregnancies with Down’s syndrome, PAPP-A, AFP and uE3 levels tend to be low and inhibin and hCG levels tend to be raised.

The level of AFP in the second blood sample is also used to determine if there is an increased risk of spina bifida or anencephaly.

Can any other abnormalities be identified?

Yes, the Serum Integrated test also identifies pregnancies at a high risk of Edward’s syndrome (trisomy 18). The risk of Edward’s syndrome can be identified using PAPP-A, AFP, uE3 and 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 you will be offered an amniocentesis.

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 for an open neural tube defect and a detailed ultrasound scan will be offered.

Edward’s syndrome

If the risk of having a term pregnancy affected with Edward’s syndrome is 1 in 100 or higher you will be offered an ultrasound scan and amniocentesis.

Performance of the Serum Integrated test using a 1 in 150 term cut-off

Down’s syndrome

Detection Rate (DR)

82% of women with pregnancies affected with Down’s syndrome will receive a screen-positive result. (The remaining 18% of women with pregnancies affected by Down’s syndrome will receive a screen-negative result.)

False Positive Rate (FPR)

2.7% of women whose pregnancies are not affected with Down’s syndrome will receive a screen-positive result. (97.3% 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)

1:12 – Among women in the screen-positive group, 1 woman will have a pregnancy with Down’s syndrome for every 12 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)

1.0%

Edward’s syndrome

Detection Rate (DR)

About 75%

False Positive Rate (FPR)

< 0.1%

Arranging a Serum Integrated test

The blood samples for the Serum Integrated test can be taken either at the Wolfson Institute of Preventive Medicine, London or by your local midwife or GP. The Antenatal Screening Service provide a sample kit which contains the necessary equipment for taking and transporting the sample. The sample should be returned in the envelope provided using the Royal Mail Special Delivery service.

To request a sample kit, make an appointment at the Wolfson Institute, or discuss the test further please contact the Antenatal Screening Service on +44 (0)20 7882 6293.

Cost

The cost of the Serum Integrated test is £120.

Information leaflets

The Antenatal Screening Service has produced two information leaflets for the Serum Integrated test.

The Questions and Answers leaflets are designed for women considering the test and contain the basic information about the screening test and the results.

The Information for Health Professionals leaflets are aimed at staff and contain more detailed information about the tests. Many women considering the tests also find this information useful.

Download the leaflets in PDF format:

See all of our Antenatal Screening Service information leaflets.

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