Amniocentisis During Pregnancy


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There are a number of tests available that allow couples and their doctors to establish the prospective health of an unborn child prior to childbirth. These techniques have been refined over recent years as technologies have advanced, but still carry with them an element of risk and controversy. One such test which is performed relatively frequently is amniocentisis, which is performed in the UK both by the NHS and by private healthcare providers.

What is amniocentesis?

Amniocentesis is also known as the amniotic fluid test, which is in turn sometimes shortened to AFT. It is a procedure which looks for any infections that may affect the foetus and for any chromosomal defects. Chromosomes are structures that carry thousands of genes, which are the blueprint for our bodies telling everything from cells to organs how they should be working. Defects in chromosomes usually result in abnormalities after birth, the most well-known of which is Down’s Syndrome, which involves an extra chromosome responsible for the condition.

How is amniocentesis performed?

Amniocentesis is so named because the test involves extracting a small amount of amniotic fluid, a substance which surrounds the foetus and acts as a protective barrier and shock absorber. Amniotic fluid has within it cells from the foetus, which can be examined in a laboratory for any signs of chromosomal damage or abnormalities.

The sample taken through amniocentesis is used for prenatal genetic diagnosis, which is the name of the test applied to foetal cells to determine their genetic health. The actual process of extracting the sample needed for this test involves inserting an extremely fine needle, under guidance from ultrasound imaging, through the wall of the stomach and into the womb. Local anaesthesia is used to spare the mother from too much discomfort, and because the needle itself is so small (keeping the puncture wound extremely small) the puncture wound will have healed within the next 48 hours. About 20ml of amniotic fluid is extracted for the test, which is also replenished quickly for the next day or two.

What does amniocentesis test for?

Amniocentesis, or more specifically prenatal genetic diagnosis, looks for chromosomal abnormalities as mentioned above. These include trisomies, where an extra copy of a particular chromosome is present and causes birth defects and developmental issues. The most well-known trisomy is trisomy 21 (an extra chromosome 21), also known as Down’s Syndrome, is tested for by amniocentesis.

This procedure also tests for a condition called rhesus disease, which is often abbreviated to RhD. Everyone’s blood belongs to one of 4 different blood groups, O, AB, A, and B, with each of these broader groups subdivided into smaller groups (e.g. A+, B-, and O-. Each of these blood groups is only compatible with other specific groups, meaning that, for example, you were to give someone with a B+ blood type any blood that wasn’t either B+ or AB+, that person would react very badly as their body would recognise the blood as being of a foreign type, and begin to attack it. Rhesus typing is another method of categorising blood types, and Rhesus Disease occurs as foetal and maternal blood are incompatible.

Are there any risks to amniocentesis?

Amniocentesis is actually fairly routinely performed these days, and is a useful provision at any antenatal care unit. The procedure still carries with it some risks however, and these are an important consideration when weighing up whether or not the benefits of having the test outweigh any potential dangers.

Because a needle is being guided into the womb, there is a risk of potential injury to either yourself or your baby. While the needle is sterilised (prepared so that it does not have any disease causing pathogens on the surface) and specially designed to make a minute puncture that is easily healed, the sensitive nature of the area means that there is always a small chance of accidentally puncturing something like the placenta. Fortunately in many cases these wounds can generally heal quite quickly.

As has been already mentioned, the needle itself is sterile and the procedure will be performed in a sterile environment, however, there is still a small chance of infection if the needle accidentally punctures your bowel, exposing you to potential disease causing agents.

Rhesus disease was discussed earlier on in this article, and if you recall this illness essentially involves an incompatibility of maternal and baby blood. There is a small chance that your blood will be exposed to the baby’s during amniocentesis, and if there is a rhesus incompatibility then this can be problematic. The risk of this happening is usually dealt with by the administration of antibodies after the procedure has been completed.

Amniocentesis also carries a small risk of miscarriage, which is the main reason why the test is only performed when there is good reason for it.

Are there any side effects after amniocentesis?

You can expect some short term side effects after the test which vary in terms of whether they occur at all and their severity. Mild cramping and pain that is quite similar to period pains are common, as well as light bleeding from the vagina (called spotting). These usually pass within a few hours, but if they persist then you must consult your doctor as soon as possible. Similarly if you feel any more severe effects like heavier bleeding, sharp contractions, or shivering then you should see a doctor straightaway.

Fortunately however in the majority of cases the aforementioned mild side effects occur and pass quickly as the body repairs the tiny puncture wound formed by the test between 24 and 48 hours.

Should I have amniocentesis?

The decision about whether or not to have amniocentesis will always be completely yours and your partners. As discussed earlier in this article, there is an element of risk involved, and as such the procedure is never performed lightly. Your doctor is not likely to suggest amniocentesis, particularly if he or she works for the NHS, unless there is a serious concern about potential chromosomal abnormalities, for instance a history of Down’s Syndrome.

Your antenatal care team’s role will be to give you all the information and support you need to make a decision about whether or not to proceed with the test.


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