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 whether a baby has a high chance of a certain chromosomal condition.
What is the SAFE test?
The St George’s Antenatal Fetal Evaluation (SAFE) test is a NIPT test is a screening test for Down’s, Edwards’ and Patau’s syndromes only, in line with UK National Screening Committee (UKNSC) recommendations. The test is performed by taking a small sample of the mother’s blood. which is then sent to the NHS laboratory at St George’s Hospital for assessment. The results are typically available within 7 calendar days from sample receipt.
How does the SAFE test work?
During pregnancy the placenta sheds cell free DNA (cfDNA) into the mother’s bloodstream. As a result, the mother’s blood contains a mixture of placental and maternal cfDNA. By evaluating the cfDNA in the blood and combining this with the mother’s background chance of a trisomy (mother’s age or the combined test results offered within the NHS), a likelihood ratio is obtained to predict whether or not the baby is more likely to have a chromosomal condition such as Down’s syndrome.
Why have the SAFE test?
As part of the national screening pathway women are offered the ‘combined test’ in the first trimester of pregnancy. This 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, the SAFE test has a higher detection rate for Down’s, Patau’s and Edward’s syndrome.
In addition if the ‘combined test’ result is available, the SAFE test is able to incorporate this to provide a more individualised result.
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 treated. 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 many young people attend mainstream schools and live fairly independent lives with varying degrees of assistance.
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 upon the child.
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.
The test is not suitable for multiple pregnancies (greater than twins), if the mother has cancer, 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, had transplant surgery, immunotherapy or stem cell therapy.
|Clinical performance of the SAFE/IONA®test in over 20,000 patient samples|
|Detection Rate||Positive Predictive Value (PPV)||Negative Predictive Value (NPV)|
|These statistics are based on post-market performance evaluation of the IONA® test in over 28,400 singleton and monochorionic pregnancies. Correct as of November 2019.|
PPVs and NPVs are specific to the population and varies by prevalence. PPVs vary based on the NIPT assay.
Detection rate – the proportion of truly affected pregnancies that are reported as high chance.
Positive predictive value (PPV) – this is the number of truly positive cases that have been identified out of all the cases that have been reported as screen positive/high chance.
Negative predictive value (NPV) – this is the number of truly negative cases that have been identified out of all the cases that have been reported as screen negative/low chance
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 chorionic villus sampling (CVS). These tests give a definite ‘yes’ or ‘no’ result as to whether your baby has Down’s, Edwards’ or Patau’s syndrome. 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.
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 invasive testing. 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
Support Organisation for Trisomy 13/18 (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 plc (The IONA® test). Yourgene Health plc 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.