Non-Invasive Prenatal Test

For the last ten years doctors have been using the results of the Nuchal Translucency Scan to advise pregnant women and their partners on their risk of having a baby with Downs syndrome, or other abnormalities. The Nuchal Translucency Scan looks at the skin fold on the back of the baby’s neck at about 12 weeks. This has been further refined by looking at the nose bone of the baby with an additional blood test to identify two pregnancy hormones.

This is the combined test and has achieved a positive predictive value of about 84%. Women with a high risk have an option to proceed to chorion villous sampling (CVS) or amniocentesis. These are invasive tests that carry a miscarriage risk of about 1:100. This is changing now that the NIPT is available. Harmony is marketed by Ariosa Diagnostics and Panorama by Natera inc. They use different techniques. In other countries there are other similar tests available: MaternitT21 by Sequenom CMM, Verifi by Verinata Health and NIFTY by BGI Health.

What is Non-Invasive Prenatal Testing?

It has been discovered that a blood sample taken from the mother at any time from approximately 10 weeks of pregnancy can be analysed for cell free fetal DNA, which is essentially a marker in the mother’s blood of the DNA of the baby. The result of the simple blood test has a detection rate of more than 99% which will hugely reduce the need for invasive testing by CVS or amniocentesis. This is great news for couples because it eliminates the risk of miscarriage of the pregnancy. It is important that an ultrasound scan is performed just before the blood test to confirm the pregnancy, and to check if the mother is carrying twins or more. NIPT can now be used in twin or more, singleton donor and surrogate pregnancies.

Who needs Non-Invasive Prenatal Testing?

Anyone who is anxious about her baby having a chromosomal abnormality such as Downs, Edwards, Patau's syndrome or a sex chromosome abnormality. It is predicted that in 10 years it will become available for all on the NHS. Women who may need it are those that are older (particularly over 40 years), have already had a chromosomally abnormal pregnancy or who are at particular risk of miscarriage should they have an amniocentesis or chorionic villous sample.

How is the test done?

• An ultrasound scan is always done first.
• This is a simple blood test from the vein in the woman's arm like any other blood test. There is no risk from having the test.
• The tubes are immediately packaged and dispatched to the laboratory.

How long does it take to get a result?

The result is usually available within 3-8 working days. There is approximately a 2% chance that no result is obtained with Harmony, 2% with Panorama and less than 1% with SAFE test. This is not a positive or negative test: it is an unsuccessful test. An offer of a repeat test is made free of charge. This is usually successful. In rare circumstances the result can take longer than 14 days. We understand it can be a stressful time waiting for results and we will endeavour to communicate any delays to our patients as soon as we receive information from the laboratory.

How is the result expressed?

The result is expressed as a probability. It is a screening test and not a diagnostic test. A result form of a low risk test is shown below. A low risk test result gives a risk of a chromosomal problem of less than 1:10000. A high risk result gives a risk of greater than 99%. A high risk result does not confirm that the baby has the chromosome abnormality. An amniocentesis or chorionic villous sampling is necessary to give a diagnosis. The couple are counselled about this.

• Harmony Test Result (Low Risk)
• Harmony Test Result (High Risk)
• Panorama Test Result
• SAFE Test Result

How much does it cost?

The test is currently £500 including the ultrasound scan when done on a weekday. Any appointment after 5.00pm carries a £30 surcharge. If you would like to come in on a Saturday or Sunday the cost is £550.

What happens after the test?

Depending on how many weeks pregnant you are, you will still have the opportunity to have a 12 week scan privately or with the NHS. The focus of the 12 week scan will change as you will already have the result of the Downs syndrome test, so the 12 week scan will look at the baby in detail for structural abnormalities (these may exist without a chromosomal abnormality). You will still have the opportunity to have the later scans, such as the 20 weeks scan, as before. If the NIPT is low risk then it is important that the person conducting the 12 week scan is aware of this. If the test is high risk then you should return to The Birth Company or a good NHS unit for further counselling.

Are there problems this test will not detect?

Yes. Structural abnormalities such as Spina Bifida, heart defects and a poorly growing baby will only be seen on scans and often not until later scans. These scans should still be undertaken.