Sickle cell and thalassaemia
Updated 3 July 2024
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This publication is available at https://www.gov.uk/government/publications/screening-tests-for-you-and-your-baby/sickle-cell-and-thalassaemia
Public Health England (PHE) created this information on behalf of the NHS. In this information, the word ‘we’ refers to the NHS service that provides screening.
This short animation explains screening for sickle cell and thalassaemia in pregnancy.
Sickle cell and thalassaemia video
1. Purpose of screening
To find out if you are a carrier of the sickle cell or thalassaemia gene and therefore likely to pass it on to your baby.
2. About these conditions
Sickle cell disease (SCD) and thalassaemia major are serious, inherited blood diseases. They affect haemoglobin, a part of the blood that carries oxygen around the body. People who have these conditions will need specialist care throughout their lives.
People with SCD can have attacks of very severe pain, get serious, life-threatening infections and are usually anaemic (their bodies have difficulty carrying oxygen). Babies with SCD can receive early treatment, including immunisations and antibiotics, which, along with support from their parents, will help prevent serious illness and allow them to live a healthier life.
People with thalassaemia major are very anaemic and need a blood transfusion every 3 to 5 weeks, and injections and medicines throughout their lives.
There are also other, less common, less serious haemoglobin diseases that may be found. SCD and thalassaemia are inherited diseases that are passed on from parents to children through unusual haemoglobin genes. Genes are the codes in our bodies for things such as eye colour and blood group. Genes work in pairs. For everything that we inherit we get one gene from our mother and one from our father.
People only have SCD or thalassaemia if they inherit 2 unusual haemoglobin genes – one from their mother and one from their father. People who inherit just one unusual gene are known as ‘carriers’ (some people call this having a ‘trait’). Carriers are healthy and do not have the disease, although they can experience some problems in situations where their bodies might not get enough oxygen, for example, having an anaesthetic.
When both parents are carriers the baby has:
- a 1 in 4 (25%) chance of not having the condition
- a 1 in 4 (25%) chance of inheriting both unusual haemoglobin genes and having the condition
- a 2 in 4 (50%) chance of inheriting 1 unusual haemoglobin gene and being a carrier
Diagram showing the chances of a baby inheriting a haemoglobin condition when both biological parents are carriers
Anyone can be a carrier of a haemoglobin disease. However, it is more common among people whose ancestors come from Africa, the Caribbean, the Mediterranean, India, Pakistan, South and South-East Asia and the Middle East.
3. The screening test
Screening in pregnancy for SCD and thalassaemia involves having a blood test. It is best to have the test before you are 10 weeks pregnant.
All pregnant women are offered a test for thalassaemia but not all women are automatically offered a test for SCD. The screening offered depends on where you live.
In areas where haemoglobin diseases are more common, you will be offered a blood test for SCD. In areas where haemoglobin diseases are less common, a questionnaire is used to identify the family origins of the baby’s mother and father.
If the questionnaire shows either parent may be a sickle cell carrier, a blood test is offered to the woman.
You can ask to have the blood test even if your family origins do not suggest your baby has a high chance of a haemoglobin disease.
4. Safety of the test
The screening test cannot harm you or your baby but it is important to consider carefully whether to have this test or not. The screening test can provide information that may mean you have to make further important decisions. For example, you may be offered further tests that have a risk of miscarriage.
5. Screening is your choice
You do not need to have the screening test. Some people want to find out if their baby has SCD or thalassaemia and some do not.
6. Not having the test
If you choose not to have the screening test in pregnancy, your baby can have newborn blood spot screening for SCD at 5 days of age.
7. Possible results
The test will tell you if you are a carrier or not, or whether you have the disease yourself.
8. Further tests
If you are a carrier of a haemoglobin disease, your baby’s father will be offered a blood test. If your baby’s father is also a carrier you will be offered diagnostic tests to find out if your baby is affected.
If your baby’s father is not available and you have been identified as a carrier, you will be offered the diagnostic test.
1 in every 200 women (0.5%) who have a diagnostic test will miscarry as a result of the test. It is up to you whether or not to have the further test. There are 2 types of diagnostic test.
CVS (chorionic villus sampling) is usually done from 11 to 14 weeks of pregnancy. A fine needle, usually put through the mother’s abdomen, is used to take a tiny sample of tissue from the placenta. The cells from the tissue can be tested for SCD or thalassaemia.
Amniocentesis is usually done after 15 weeks of pregnancy. A fine needle is passed through the mother’s abdomen into the uterus to collect a small sample of the fluid surrounding the baby. The fluid contains some of the baby’s cells, which can be tested for SCD or thalassaemia.
9. Possible results of diagnostic tests
If the result shows that your baby has SCD or thalassaemia then you will be offered an appointment with a health professional. You will be able to get information about the condition your baby has inherited and talk through your choices.
Some conditions are more serious than others. Some women decide to continue with the pregnancy. Others decide they do not want to continue with the pregnancy and have a termination.
If you are faced with this choice you will get further information about the condition and support from health care professionals to help you make a decision. Information is also available from support organisations.
If the test shows that you are a carrier, there is a chance that other members of your family could be carriers too. You may want to encourage them to ask for a test, especially if they are planning to have a baby.
10. Getting results of diagnostic tests
The person doing the test will discuss the arrangements for providing your result.
Find more information and details of support groups on NHS.UK.