What you need to know before having a baby: Carrier Screening in simple terms

Are you and your partner thinking about having a baby? Or are you already pregnant? Then what we are going to talk about today will be very important for you. Sometimes, even if we are completely healthy, we may have hidden changes in our bodies, that is, in our genes, related to certain diseases. This is when we are said to be a 'carrier' of a certain disease. Today we are going to talk about 'carrier screening', which is done to find out if we are a carrier.

Simply put, what does it mean to be a 'carrier'?

Think about it, for every characteristic in our body (e.g. hair color, eye color), we have two copies of the gene. One we get from our mother, the other from our father. A 'carrier' is someone who has a small defect or change (pathogenic variant) in one of the two copies of the gene that is associated with a certain disease.

But, because the other copy of the gene is healthy, it 'subdues' the function of the one with the defect. So you don't show any symptoms. You are healthy. But you have the potential to pass on this defective gene to your children. That's what you're called a 'carrier'.

Most of the time, these carrier tests look for diseases that are inherited in an 'autosomal recessive' way. This means that for a child to have the disease, both parents must be carriers of the disease. In most cases, no one knows they are a carrier. This is because no one in the family may have the disease.

In addition, there is a category of genetic diseases called 'X-linked' conditions. These are inherited through sex chromosomes. These are also tested for by some carrier tests.

When is this carrier screening done? Why is it important?

The best and most appropriate time to have this test is before you even plan to get pregnant. That way, you have plenty of time to make decisions about your future based on the results, without any worries and with peace of mind.

Imagine, if you found out that you were both carriers of the same disease, you could think of different options.

• Creating a child using someone else's egg or sperm (IVF using donor eggs or sperm).
• Preimplantation genetic testing involves testing the embryo's genes and implanting only a healthy embryo into the uterus.
• Adoption of a child.

If you were unable to get this test done before you became pregnant, you can still get it done during the first trimester of your pregnancy. Even then, you will have the opportunity to plan your future pregnancy based on the results and, if necessary, have further tests, such as amniocentesis, to confirm the baby's condition.

What kind of diseases does this test look for?

Carrier testing looks for several common genetic diseases. Some of them are:

• Cystic fibrosis
• Sickle cell disease
• Thalassemia - This is a relatively common condition in Sri Lanka.
• Tay-Sachs disease
• Fragile X syndrome

In addition to these, there are now tests called 'Expanded carrier testing' that can test for dozens of other diseases at once. If someone in your family has a specific genetic disease, you can also have a test that is targeted for that disease (Targeted carrier screening). You can discuss all of these with your doctor and decide.

How is the test done? Is it a big deal?

This test is usually performed using one of the following methods:

• Blood test: A small amount of blood is taken from your arm.
• Saliva test: A small amount of your saliva is collected in a tube.
• A tissue test: A small swab is used to swab the inside of your cheek .

If a sample is being taken from saliva or a cheek swab, you may be advised to refrain from eating or drinking for a short period of time before the test. Other than that, no special preparation is needed.

What do the results say? How do we understand it?

Your sample is sent to a special genetics lab for testing. It can take a few days or weeks for the results to come back.

If the result is 'Negative'...

This means that the genetic defects related to the diseases you were tested for were not found in you. This means that the risk of your children developing those diseases is very low. But it cannot be said that it is 100% zero, because these tests may not be able to catch all genetic defects. But knowing that the risk is very low can give you a great sense of relief.

If the result is 'Positive'...

This means that you are a carrier of one or more genetic diseases. Don't be alarmed when you hear this. This does not mean that you have a disease. You are still healthy.

But the most important thing to do at this time is to have your partner tested for the disease as well.

What if you are both carriers of the same disease?

This is where we need to focus. If you and your partner are both carriers of the same autosomal recessive disease, here are the chances that each child you have will be affected:

Once you receive these results, your doctor will refer you to a Genetic Counselor , a person with special training and knowledge in genetic diseases. He or she will explain the situation to you further, answer your questions, and discuss possible next steps.

Are there any risks to this test?

Physically, there are no major risks other than feeling a slight stinging pain when having blood drawn.

But you also need to think about the psychological side. Some people may feel a little stressed and anxious about getting tested and getting the results. And very rarely, you may find out that you are not only a carrier, but also have a very mild form of the disease. So talk openly about all of this with your doctor before the test. If you are feeling emotionally uncomfortable, don't hesitate to tell your doctor about it.

Carrier Screening, Genetic Testing, Carrier Testing, Pregnancy, Thalassemia, Sickle cell disease, genetic testing, pregnancy, family planning