Nuchal Translucency Scan
Talking of earlier diagnosis, is this available if wanted?
This is an area where a lot of research- continues to take place and some promising results are starting to emerge.
In the UK, a few years ago, a large study coordinated by the Harris Birthright Research Centre for Fetal Medicine looked at offering women early screening for Down's and other chromosomal genetic abnormalities in the first trimester (11-13 weeks). This is by using ultrasound to measure the thickness of the back of the fetal neck (also known as nuchal translucency). This was used in several hospitals in and around London with quite promising results. Similar studies took place in other centres in the UK as well as other countries.
The basis for this screening test is the known fact that, around this gestation, fetuses with a variety of chromosomal defects tend to have increased thickness of the nuchal pad (the skin at the back of the neck). When this is measured and found to be increased (more than 3 mm), it triggers the suspicion of something amiss (which could be Down's or some other condition).
This finding should prompt a careful and thorough search for other physical or organic abnormalities associated with these syndromes.
The mother may then be offered a diagnostic test to definitively establish the truth. The expected benefit of this is that the diagnosis is established much earlier and if the fetus is affected, it is assumed that any decision to terminate the pregnancy will be comparatively less difficult and probably less traumatic.
How effective is this early screening test?
The results are impressive but it is by no means infallible. Preliminary results indicated that it may have a sensitivity of between 65 and 80 per cent, comparing quite favourably with the established screening (blood) tests. Moreover, it has been observed that, if the nuchal pad thickness is more than 6 mm, the possibility of an abnormality (Down's or otherwise) is as high as 93 per cent. This is now part of the screening ‘integrated test’ mentioned earlier.
The nuchal translucency scan test was initially available privately in most parts of the UK and has since been made available as part of the standard service in all NHS hospitals and is accessible free, like all other maternity services, to every woman. The test can also be accessed throughout the world where the expertise and equipment are available
Is there any prospect of a definitive diagnosis test that is non-invasive?
This is a very attractive idea, since it will eliminate the risk of miscarriage as a consequence of the diagnostic test. A lot of research work has gone on for years concentrated on utilising fetal cellular material which can be isolated from the mother’s blood. The idea is to take a blood sample from the mother, isolated fetal cellular material that is normally found there (in minute quantities) and process it to analyse the chromosomal make-up of the fetus.
There are some successes increasingly reported in this area.We have discussed this in more detail here and here: