A blog considering the present screening for Down Syndrome and the potential benefits and limitations of a new form of screening presently being trialled.
I have been reading a great deal of discussion in the media this month in relation to the screening tests that are available to determine the risk of a baby being born with Down Syndrome (also known as Down’s Syndrome or Downs). Trials involving 2,500 women have been carried out by a specialist team at Great Ormond Street Hospital (GOSH). The team have now announced that the tests could be both cost effective and reduce the risk of miscarriage.
The quest for non-invasive testing has long been the focus of research in Genetics and Fetal Medicine. The blood tests that are currently carried out in screening for Down Syndrome test the levels of hormones in the mother’s blood rather than the baby’s own DNA.
A mother’s blood does contain her babies DNA and recent developments in technology have now allowed very precise separation of the baby’s DNA from the mother’s blood. This new form of testing, Non-Invasive Prenatal Testing (NIPT), will allow testing for many genetic disorders.
In the UK women are offered a ‘combined test’ which includes an ultrasound and a blood test to assess the risk of their baby having Downs. These tests are carried out between 11 and 14 weeks gestation.
If the mother is too far along in her pregnancy, after 14 weeks + 1, a later screening test can be offered up to 20 weeks. This test consists of a maternal blood test only.
These screening tests are non-invasive and, for the majority of women, the end of the line for worries about Down Syndrome.
However, for some women screening results will identify that the baby is in the high risk category of developing Down Syndrome. This then leads to the extremely difficult decision of whether to have a diagnostic test to give a more definite answer.
There are two types of diagnostic tests available, both of which carry a risk of miscarriage. Approximately 1 in every 100 women who have a diagnostic test will have a miscarriage as a result.
The most common diagnostic test available is amniocentesis. This is where a fine needle is inserted through the Mother’s skin in to her womb and a small amount of amniotic fluid (the fluid that surrounds the baby) is removed for testing.
The new testing is reported to have a number of potential benefits:
• Speed – It can be carried out as early as 10 weeks gestation and the results can be returned within a matter of days rather than the fortnight that the current testing results can take.
• Accuracy – The team at GOSH have stated that NIPT is 99% accurate in testing for Downs, which is a huge jump from the current tests of which the accuracy percentage is only 75%. There is also a reduced risk of false positives, from 3% (combined test) to 1% (NIPT).
• Cost – In the UK NIPT is currently only available privately and can cost up to £1,200. Though NIPT is costly the research has shown an 80% drop in the number of women requiring amniocentesis. This in itself will greatly reduce costs due to less costly diagnostic tests being carried out.
• Risk – Due to the fact that NIPT is more accurate and has increased the detection of affected babies the GOSH Team have seen a rapid drop in the number of women needing/wanting invasive testing to rule out Downs. This means that less women will unnecessarily undergo invasive tests when in fact there baby does not have Downs. Women who would never consider testing due to invasive tests may consider NIPT due to the reduced risk factor.
NIPT will not be available for multiple pregnancies due to the combination of blood that will appear in the mother’s blood, unless the babies are identical twins.
Due to the fact that a 1% risk of a false positive exists, women who do show as having a high risk of having a baby with Downs will still have to make the decision of whether to have a further diagnostic test. However they will now have more accurate information with which to make their decision.
The UK’s National Screening Committee is set to examine the results this month in order to determine whether NIPT can be made available through the NHS. The current considerations in play involve adding NIPT as a step in the current screening process.
The Royal College of Obstetricians and Gynecologist’s (RCOG) have reported opinion that NIPT will become the primary screening test for chromosomal abnormalities in the future and that this will both enhance the information available to pregnant women and cut costs.
Here at the Clinical Negligence Team we sometimes have to advise clients who have been given wrong information about the results of these screening tests and were falsely reassured that their baby did not have a condition they are then subsequently born with. As a result the parents lost the opportunity to make informed decisions and plans during the pregnancy. These new tests sound very positive in terms of the level of accuracy they will offer and will hopefully reduce incidents where parents are given wrong information accordingly, and I will follow the developments with interest.