Learn about the prenatal testing in Sickle Cell Disease that parents with AS genotype could consider to
Dear Dr, I am actually dating and I have got to realise that we are both AS. We want to know about early detection and how the status of the undeveloped fetus can be assessed to see if there’s no SS….
Please, how can this be done and which countries can do these tests? – Name withheld
Sickle Cell Disease (SCD) is an inherited condition present from birth.
A person develops sickle cell disease if they are the offspring of 2 people with the AS genotype (sickle cell carrier); or two people with Sickle Cell Disease, SS genotype.
It is a serious medical condition that affects the blood cells.
In a person with SCD, the usual round/circular red blood cells are replaced by abnormal 'C-shaped' sickle cells, which tend to stick together easily.
This causes a lot of problems with blood flow and can lead to severe pains in the joints and organs, the development of anaemia and other serious medical problems - read more.
Though present from birth, it does not start to express
itself with symptoms until at least 6 months.
Development of Haemoglobin type
And, this delay is because of the ‘type of blood’ circulating between birth and 6 months.
Haemoglobin is the protein that carries oxygen on red blood cells.
In most people, the normal circulating haemoglobin is
When you have SCD, your haemoglobin type is Haemoglobin S.
While still in the womb, the blood type within the baby is Haemoglobin F, the foetal h
After birth, we would all still have our Haemoglobin F as the major blood type for a short period of time.
Then it starts to be replaced by the adult type – Haemoglobin A; unless the individual has the Sickle genes in which case Haemoglobin F is replaced by Haemoglobin S.
Usually this happens from 4 months onwards.
Therefore, this is why generally we will not find symptoms of SCD in a child till they are above 6 months when they now have their ‘adult’ haemoglobin.
So why Prenatal Testing in Sickle Cell Disease ?
Prenatal testing in sickle cell disease is what happens when tests are conducted on your baby prior to birth when you and
There are several types of prenatal tests – that are either non-invasive
They are used for detecting abnormalities that exist before birth – including genetic problems such as Sickle Cell Disease.
Prenatal Tests for Sickle Cell Disease and when they are used
Currently, there are mainly 2 prenatal tests for diagnosing Sickle Cell Disease:
- Amniocentesis and
- Chorionic Villus Sampling (CVS)
Both are invasive tests.
This means that there would be access into the body cavity of either the mum or baby (or both) in order to perform the tests.
This could result in specific complications (see below).
Now, before we discuss the tests, it is important to be clear on why they are being performed.
As we said earlier, the tests are performed to identify
abnormalities before the child is born.
Not every pregnant woman needs to have the tests.
However, if you have a risk of bearing a child with SCD, the tests may be considered by the parents to determine if their baby has the condition and how they may proceed.
The results of the tests are crucial because they will mean you, as a couple will need to decide whether to continue with the pregnancy or not.
In the case of a child with SCD, continuing the pregnancy may require tough decisions – see here; or deciding to terminate (abort) the pregnancy.
Therefore, before undergoing Prenatal Testing, counselling
Counselling before prenatal testing
Counselling would consider
- the need for the tests – identify why your child may be at risk;
- the entire process of the test including the risks and complications;
- and the subsequent decisions or choices to be made and living with them.
Risks associated with Prenatal tests
Both tests mentioned above are carried out early in pregnancy.
They involve taking liquid or tissue sample from the amniotic sac carrying your baby or around the placenta and testing the cells from the sample to identify abnormal genes.
- In this test, a needle is introduced through the mum’s abdomen into the womb and amniotic sac – under ultrasound guidance.
- This means that as the needle is entering the womb and the sac, the specialist is watching its progress on the screen to avoid any injury to the organs.
- Once within the amniotic sac, a small amount of amniotic fluid is withdrawn via the needle.
- The amniotic fluid is the liquid material in which the baby swims and lives all through the pregnancy.
- Skin cells from the baby are shed into the amniotic fluid and it is these cells that are examined from the sample collected during amniocentesis.
- Now the test is usually carried out in the 2nd trimester; no more than 15-16 weeks.
- It takes a few weeks for the cells to be cultured in the laboratory to identify abnormal genetic material.
- The risks associated with Amniocentesis are:
- Infection to Mum and/or Baby
- Bleeding from Mum and/or Baby
- Damage to organs
close by Miscarriagefollowing the test.
While these are possible risks, it must be said that at very reputable facilities and with experienced specialists, these risks can be minimised.
- Chorionic Villus Sampling
- This test is carried out at an earlier stage in pregnancy – usually from 11-14 weeks.
- During the test, a fine needle, usually put through the mother's tummy, is used to take a tiny sample of tissue from the placenta. This is the transabdominal approach.
- Another way of getting the sample from the placenta is through the neck of the womb and this is reached via the vagina – the transcervical approach
. Again, the possible risks are infection, bleeding or miscarriage – like what may happen following Amniocentesis.
Finally, the emotional toll of these procedures is an important aspect that must be considered.
It is important to be clear that when an AS genotype couple
are pregnant, the risk of the child developing SS is 25%.
This means that for every pregnancy they have there is a 1:4
chance the child will have SCD every single time.
How many times can a couple undergo the tests? What if it is positive every time?
How many times will a termination be done?
Such outcomes must be considered and discussed by the couple when in this situation.
The decision about having these tests is for the
However - and crucially, they must have access to clear explanations about the procedure, risks and possible outcomes to do so.
We will recommend that if you wish to have the procedure, ensure it is with a reputable, well-equipped facility, and by a specialist who has the relevant expertise.
Are you interested in learning more about this condition? Comment below or share your experiences.
Editing by AskAwayHealth Team
All AskAwayHealth articles are written by practising Medical Practitioners on a wide range of health care conditions to provide evidence-based guidance and to help promote quality health care. The advice in our material is not meant to replace the management of your specific condition by a qualified health care practitioner.
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