Learn about the prenatal testing in Sickle Cell Disease that parents with AS genotype could consider to know if their unborn child has the condition.

Dear Dr, I am in a serious relationship and we are both AS. We want to know about early detection and how to check the baby to see if they are SS….
Please, how can this be done and which countries can do these tests? – Name withheld

Introduction

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.

How You Develop a 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 Haemoglobin A.

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 haemoglobin.

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.

Why Prenatal Testing for 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 your partner are AS genotype to determine if the baby has the SS gene.

There are several types of prenatal tests – that are either non-invasive or 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 to use them

Currently, there are mainly 2 prenatal tests for diagnosing Sickle Cell Disease:

1. Amniocentesis and
2. Chorionic Villus Sampling (CVS)

Both are invasive tests. 

This means that there would be access to 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.

Counselling before Prenatal Testing

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 is important.

 Counselling would consider issues like:

• 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 samples from the amniotic sac carrying your baby or around the placenta and testing the cells from the sample to identify abnormal genes.

• Amniocentesis
  • In this test, a needle passes 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, the needle allows doctors to withdraw a small amount of amniotic fluid for testing.
  • The amniotic fluid is the liquid material in which the baby swims and lives all through the pregnancy.
  • Skin cells from the baby are present in the amniotic fluid and we examine these cells from the sample collected during amniocentesis.
  • You will have the test in the 2^nd trimester; no more than 15-16 weeks.
  • Afterwards, it takes a few weeks to culture (grow) the cells 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
    • Miscarriage following the test.

• Chorionic Villus Sampling
  • You will have this test at an earlier stage in pregnancy – usually from 11-14 weeks.
  • During the test, doctors use a fine needle, usually put through the mother’s tummy, 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. Your doctor can do so via the vagina – the transcervical approach.
  • Again, the possible risks are infection, bleeding or miscarriage – like what may happen following Amniocentesis.

While these are possible risks, couples can reduce the chance of things going wrong by visiting specialist centres for the proceedure.

What comes after the tests?

Finally, the emotional toll of these procedures is an important aspect to consider.

It is important to be clear that when an AS genotype couple is 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.

A couple may get pregnant 6 times and in each case, all the children have the SS gene. Or none have the SS gene.

• How many times can a couple undergo the tests?
• What if it is positive every time?
• How many times can they have a termination?

It’s important to consider such possibilities and discuss them (and any others) at meetings with your specialists.

The decision about having these tests is for the prospective parents to make.

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.

 Do you want to learn more about this condition? Comment below or share your experiences.

More Reading

• Please Help! After Sickle Cell Anaemia Diagnosis, What Comes Next?
• Chance of SS genotype with AS parents?
• Sickle Cell Disease and Anaemia – Know the Difference
• Haemoglobin C Disease : Which is worse – SC or SS genotype?
• AS Genotype – 7 point Checklist

Editing by AskAwayHealth Team

Disclaimer

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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