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The integrated test

The Integrated test is the most effective method of screening for Down's syndrome as it looks at all of the screening markers from both the first and second trimesters of pregnancy.

This page explains:

What does the integrated test involve?

The 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 of pregnancy, but between 14 and 22 weeks is acceptable.

The first stage involves:

      An ultrasound scan examination to precisely determine the gestational age of the pregnancy and to measure the nuchal translucency (NT) thickness, a space at the back of the baby's neck.
      Taking a sample of your blood to measure the concentration of pregnancy associated plasma protein-A (PAPP-A).
      Providing you with a recommended date for taking a second blood sample for the second stage of the test.

The second stage involves:

      Taking a blood sample to measure the concentration of the following four markers:
    1. alpha-fetoprotein (AFP)
    2. total human chorionic gonadotrophin (hCG)
    3. unconjugated oestriol (uE3)
    4. inhibin-A (inhibin)
      Integrating the measurements from the first and second stages into a single screening result. The NT measurement and 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 nuchal translucency measurement, 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.

Why wait until the second stage to have a risk estimate?

Because by using information from both stages the test is safer and more effective than a test using information form the first stage alone. It will distinguish affected from unaffected pregnancies more effectively, reducing the chance that a Down's syndrome pregnancy is missed as well as reducing the chance that you will need an invasive diagnostic test, such as amniocentesis or chorionic villus sampling (CVS).

Can any other abnormalities be identified?

Yes, the Integrated test also indentifies pregnancies at a high risk of Edwards' syndrome (trisomy 18). The risk of Edwards' syndrome can be identified using NT, PAPP-A, 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 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.

Edwards' syndrome

If the risk of having a term pregnancy affected with Edwards' syndrome is 1 in 100 or higher you will be offered another ultrasound examination and amniocentesis.

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

Down's syndrome

Detection Rate (DR)

90% of women with pregnancies affected with Down's syndrome will receive a screen-positive result. (The remaining 10% of women with pregnancies affected with Down's syndrome will receive a screen-negative result.)

False Positive Rate (FPR)

1.3% of women whose pregnancies are not affected with Down's syndrome will receive a screen positive result. (98.7% 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)

1:5 – Among women in the screen-positive group, 1 woman will have a pregnancy with Down's syndrome for every 5 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%

Edwards' syndrome

Detection Rate (DR)

About 85%

False Positive Rate

< 0.1%

Age specific performance for Down's syndrome

Maternal age group (years Probability of screen-positive result Proportion of Down’s syndrome pregnancies detected (%)
Under 25 1 in 100 85
25-29 1 in 90 86
30-34 1 in 50 89
35-39 1 in 20 94
40-44 1 in 8 97
45 and over 1 in 5 98
All 1 in 63 90
(mid-trimester estimates of performance, first stage performed at 11 weeks GA)

Performance of the Integrated Test using fetal Nasal Bone at a 1 in 150 term cut-off

In some centres (including the London Ultrasound Centre) the NB is measured along with the nuchal translucency (NT) at the first trimester ultrasound scan. In pregnancies affected by Down’s syndrome the nasal bone tends to be absent.

Down’s syndrome

Detection Rate (DR)

94% of women with pregnancies affected with Down’s syndrome will receive a screen-positive result. (The remaining 6% of women with pregnancies affected by Down’s syndrome will receive a screen-negative result).

False Positive Rate (FPR)

1.0% of women whose pregnancies are not affected with Down’s syndrome will receive a screen-positive result. (99% 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)

1:4 – Among women in the screen-positive group, 1 woman will have a pregnancy with Down’s syndrome for every 4 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 85%

False Positive Rate (FPR)

< 0.1%

Arranging an Integrated test

The ultrasound scan and blood sample for the Integrated test are performed at the London Ultrasound Centre. The analysis and interpretation are performed by the Antenatal Screening Service at the Wolfson Institute. For further information please contact the London Ultrasound Centre on +44 (0)20 7935 4450.

Cost

The cost of the Integrated test at the London Ultrasound Centre is from £225. This includes the first trimester scan to measure the NT and NB and the two blood samples.

Information leaflets

The Antenatal Screening Service has produced two information leaflets for the Integrated test and two for the Integrated Test using fetal Nasal Bone.

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:

Integrated test

Integrated Test using fetal Nasal Bone

This test is performed at the London Ultrasound Centre.

See all of our Antenatal Screening Service information leaflets.

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