Biochemical Screening and Late Down Syndrome Screening
‘Biochemical Screening’ is part of the first trimester screening for which I have written an article on this issue and will not go into detail. Biochemical screening is just the analysis of blood with nothing more, as its very name suggests. Since returning to Bulgaria, unfortunately, I have observed a very worrying trend and an incorrect understanding of the results.
When getting the result of the combined screening test, which is the correct term, several indicators are important, but the most important is the final result. When interpreting a result, we look at the initial risk, which is based solely on the age of the woman and the final risk, i.e. the combined risk. In most laboratories, they also provide a biochemical risk that does not really exist because there is no study that validates this risk, and it is not the final one! This means that we should not pay any attention to it!
The starting point is the risk based on the age of the woman, and the combined risk is important!
Interpretations of the risk and blood counts are also interesting! Unfortunately, many of these interpretations are very simple and in most cases even startling for future parents! Numermous times I have heard from parents that lab workers tell them:
‘This indicator is very low/high! You must/it is good to repeat the analysis with a later screening!’
‘Your risk is high! Your risk is low, but ... You must/it is good to have a late screening!’
Unfortunately, the interpretation in these cases is not only elementary and without any understanding, but it also involves psychological coercion and the obligation of the pregnant woman to do something against her interest!
Here are the facts:
Combined screening test, when a correct history is taken from the pregnant woman, the echography is done by a certified specialist, the blood test is done by a laboratory with the appropriate technique that goes through regular quality control, then we have 90-95% confidence in the result for Down syndrome and 5% false positive frequency. I.e., Out of 100 babies with Down Syndrome, we will find 90-95, and every 5 out of 100 women will have a high risk without having the baby affected.
The late screening in Bulgaria is a triple test, in the same of the above mentioned conditions we will get 50-60% reliability result with a false positive frequency of up to 20%. Late screening is a much more inaccurate test than the combined one and afterwards the most unnecessary amniocentesis are made!
A late Down syndrome screening is done only when the combined screening test is omitted.
When receiving a high risk from the combined screening test, there is NEVER a late screening made! There are other methods to continue with until a satisfactory result is obtained.
When you get mixed results from biochemistry (blood), they need to be interpreted adequately and then evaluate the follow-up actions! It’s too simple to decide everything with a late screening!
Why is it important to have an echography performed by a trained and certified specialist and laboratory? At the end of the 90’s, an audit was carried out in all the laboratories that carried out this test in the UK. It turns out that some of them do not give correct data. These laboratories are forbidden to continue doing this test. There are several labs in the country that maintain a high level. Fetal medicine specialists know who these labs are and work only with them.
Fetal Medicine Specialists are aware of how to interpret the result as a whole - from echography, biochemistry and risk! You get full consultation, without any unnecessary details, but without missing any significant things! The fact that someone has an expensive and modern ultrasound does not make him a specialist! Only training and knowledge makes someone a specialist!