Non-Invasive Prenatal Testing (NIPT) – The SAFE Test
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What is NIPT?
Non-Invasive Prenatal Testing (NIPT) is a blood test taken from the mother in pregnancy, that uses cutting edge DNA technology to evaluate accurately whether a baby has a high chance of a certain chromosomal condition.
What is the SAFE test?
The SAFE test is a non-invasive prenatal test (NIPT), which is performed by taking a small sample of the mother’s blood. The blood is then sent to the laboratory for assessment with results typically available within 5 working days from sample receipt. The SAFE test has a accuracy rate of over 99% for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome.
How does the SAFE test work?
During pregnancy the placenta leaks DNA into the mother’s bloodstream. As a result, the mother’s blood contains a mixture of placental and maternal DNA. By looking at the placental DNA in the mother’s blood, the SAFE test is able to predict whether or not the baby is more likely to have a chromosomal condition such as Down’s syndrome.
What is Down’s syndrome?
People with Down’s syndrome (or Trisomy 21) have an extra copy of chromosome 21 (three chromosome copies rather than the usual two). Around one in every 1000 babies born in the UK will have Down’s syndrome and there are over 40,000 people in the UK with the condition. Anyone can have a baby with Down’s syndrome, although the chance increases for older mothers, most babies with Down’s syndrome are born to younger women.
Down’s syndrome is a life-long condition typically associated with some level of learning disability. Some health conditions are more common in people with Down’s syndrome. Although most medical issues can be fixed, Downs’ syndrome is extremely variable and it is impossible to know what life will be like for you and your baby. Some children and adults will need long term support, however most adults live fairly independent lives from their families.
Can the SAFE test screen for all conditions?
No-Down’s syndrome is the most common condition looked for as well as two rarer and conditions known as Edwards’ syndrome (trisomy 18) and Patau’s syndrome (trisomy 13).
What are Edwards’ and Patau’s syndrome?
Edwards’ and Patau’s syndromes are life limiting conditions and will cause a wide variety of developmental and health difficulties, some of which can be very serious. Around 70% of pregnancies affected by Edwards’ and Patau’s syndrome will end in miscarriage or stillbirth. Partial forms of Edwards’ and Patau’s syndrome have a lesser impact.
Who can have the SAFE test?
The test is suitable from 10 weeks of pregnancy for all single and identical twins pregnancies, including IVF, egg donor or surrogate pregnancies. For non-identical and ‘vanishing twin’, test sensitivity is reduced from 99% to 95%.
The test is not suitable for multiple pregnancies (greater than twins), or if the mother has cancer or a chromosomal or genetic condition (including Down’s syndrome). It is also unsuitable for mothers who have undergone a blood transfusion in the last 3 months, or had transplant surgery, immunotherapy or stem cell therapy.
|Clinical performance of the SAFE/IONA®test in over 20,000 patient samples|
|Overall accuracy: >99%||No call rate: <0.5%|
|The IONA® test|
|Sample status||Results||Detection Rate|
|Based on post-marketing surveillance. Only singleton pregnancies included.|
PPV is specific to the study population.
Detection rate – the proportion of truly affected pregnancies that are reported as high chance.
Positive predictive value (PPV) – the likelihood that a high chance test result means the pregnancy is truly affected with a trisomy.
How does the SAFE test differ from the usual ‘combined test’?
The ‘combined test’ and the SAFE test are very different; both in how they are performed and in the accuracy of their results. The ‘combined test’ evaluates hormonal blood levels with ultrasound findings, to assess the chance of chromosomal or structural anomalies. Although the range of conditions that can be detected by this method is broader than the number of conditions identified by the SAFE test, it is not as accurate as the SAFE test for detecting baby’s with Down’s syndrome (85% detection rate compared with 99% with the SAFE test).
Where does amniocentesis and CVS fit in?
Traditionally, if you were to receive a “high chance” result following the combined test you would be offered an invasive procedure such as amniocentesis or chorionic villus sampling (CVS). Both procedures involve using a fine needle to collect either a small sample of the amniotic fluid that surrounds the baby (amniocentesis) or a small sample of cells from the placenta (CVS).
Although these invasive procedures give a definitive diagnosis they do carry a small risk of miscarriage. The chance of miscarriage is often a dilemma for parents, with many women opting to have NIPT, such as the SAFE test before proceeding to an invasive procedure.
How is the SAFE test reported?
Low chance: means that it is very unlikely that your pregnancy is affected by trisomy 21, 18 or 13, and therefore very unlikely that your baby has Down’s, Edwards’ or Patau’s syndrome.
High chance: means that there is an increased chance that your baby will have trisomy 21, 18 or 13 and that the result should be confirmed by an invasive diagnostic test.
No call result: in a very small number of cases (1 in 200) tests may not yield a result for a variety of reasons. In this instance the clinical team will discuss your available options.
What happens if I get a “high chance” result?
If the SAFE test result shows a high chance of a chromosomal condition you will be offered an invasive diagnostic test such as amniocentesis or CVS. These tests give a definite ‘yes’ or ‘no’ result as to whether your baby has Down’s, Edwards’ or Patau’s syndrome.
It is important to remember that NIPT is a screening test which means that occasionally false positive and false negative results do occur. It is a good idea to consider the need to be certain about the diagnosis compared to the risk of miscarriage associated with the invasive procedure. Some women, who would continue their pregnancy anyway, may be happy to proceed without an invasive test. An invasive test would be needed to confirm the SAFE test result for those considering termination of pregnancy.
Your midwife and/or obstetrician will be on hand to answer any questions you may have and to support you through this time.
Who can I contact for further information?
If you have any questions about the SAFE test, please contact your named midwife or consultant obstetrician. To contact directly, please email: theSAFEtest@nhs.net
Other useful organisations
Down’s syndrome Association
Tel: 020 8682 4001
Tel: 07814 929306
Supporting organisation for Trisomy 13 and Trisomy 18 (SOFT) UK
Antenatal results and choices (ARC)
Tel: 020 7631 0285
About St George’s University Hospitals NHS Foundation Trust
The maternity unit at St George’s University Hospitals NHS Foundation Trust is a regional and tertiary referral unit ranking one of the safest in the country. Delivering over 5,000 babies each year, the unit has achieved exceptional clinical outcomes, the highest possible external accreditation and boasts the highest ‘midwife: birth’ ratios in London. The unit has consultant and midwifery led maternity care and state of the art equipment, including neonatal intensive care and a special care baby unit.
The Fetal Medicine Unit at St George’s Hospital is a leading tertiary referral centre and research centre located within a purpose built unit. It houses state of the art facilities for all aspects of care from routine assessment up to invasive procedures, including fetal surgery (surgery in the womb). The unit routinely accepts referrals from the 10 district general hospitals in the south-west London region including approximately 35,000 women a year for antenatal care. Extra-regional referrals are also received for complex fetal surgical procedures and maternal care from other hospitals in the UK and Europe. The unit has recognised international expertise in the clinical and supportive management of high-risk care in pregnancy.
Media coverage of the SAFE test
- BBC Radio 4 Today programme – May 2016
- Guardian – January 2016
- ITV News – January 2016
- BBC News – January 2016
- The Mirror – January 2016
- The Express – September 2015
- Mums net – August 2015
- Tooting Daily Press – June 2015
- Financial Times Magazine – April 2015
- Daily Mail – March 2015
The SAFE test is a CE-marked in vitro diagnostic test from Yourgene Health (The IONA® test). Yourgene Health is a UK based molecular diagnostics company working in partnership with St George’s University NHS Hospitals Foundation Trust to create a UK Centre of Excellence in bringing the first regulated NIPT test to more pregnant women.