Section 4 – Screening for sickle cell and thalassaemia in pregnancy
This section explains the tests you can have during pregnancy to find out if you are a carrier of sickle cell or thalassaemia. If you are a carrier, the father of your baby will also be offered testing. There are a number of different types of carrier.
This animation gives information on the screening tests you will be offered during pregnancy for you and your baby.
What are sickle cell disorders and beta thalassaemia major?
Sickle cell disorders and beta thalassaemia major are serious inherited blood conditions. They affect the haemoglobin in the red blood cells. Haemoglobin is important because it carries oxygen around the body. People who have these conditions will need specialist care throughout their lives. There are also other, less common haemoglobin disorders. Many of these are not as serious.
If you and the father of your baby are both carriers of ‘important types’ of sickle cell or thalassaemia, your baby could inherit a sickle cell disorder or thalassaemia major.
Sickle cell disorders
People with a sickle cell disorder can:
- have tissue and organ damage and varying degrees of symptoms
- have attacks of severe pain where they need to stay in hospital, and
- be more prone to serious infections
Beta thalassaemia major
People with beta thalassaemia major have:
- severe anaemia and need blood transfusions every four to six weeks as well as other treatments.
How are the disorders inherited?
Sickle cell and thalassaemia are genetic disorders. They are passed on in families. If only one parent (either the mother or father) has the sickle cell or thalassaemia gene, it is very unlikely that their baby will have a sickle cell disorder or thalassaemia major. But their baby may be a carrier.
This means that, like the mother or father, the baby will have the sickle cell or thalassaemia gene, but the gene does not usually cause problems. If you and the father of your baby are both carriers of ‘important types’ of sickle cell or thalassaemia, your baby could inherit a sickle cell disorder or thalassaemia major.
If both parents carry a sickle cell or thalassaemia gene, the baby may have a 25% (one in four) chance of having a sickle cell disorder or beta thalassaemia major.
If you and the father of your baby are both carriers of ‘important types’ of sickle cell or thalassaemia, your baby could inherit a sickle cell disorder or thalassaemia major.
Who can be a carrier of sickle cell or thalassaemia?
Anyone can be a carrier of sickle cell or thalassaemia. The chances of being a carrier of sickle cell or thalassaemia are higher for certain groups of people.
You are more likely to be a carrier if your family, no matter how many generations back, come from the Mediterranean, Africa, the Caribbean, the Middle East, South Asia, South America or South East Asia.
The test
The test is a blood test which can be done with other blood tests, usually early in pregnancy. The test is only offered to women with a higher chance of carrying sickle cell or thalassaemia. See ‘Who is offered the test?’ to see if you are in this group. As part of your antenatal care, you will be offered a routine blood test (a full blood count) to check your haemoglobin level to see if you are anaemic.
The full blood count can also find some types of thalassaemia. The midwife will ask you if you would like to have thalassaemia screening as part of the full blood count test. If your full blood count test suggests that you might carry thalassaemia, the laboratory may also screen your blood for sickle cell disorders and thalassaemia.
Who is offered the test?
Your midwife will ask you about your family origins. You should be offered the test if:
- you or the biological father of your baby has a family history of sickle cell or thalassaemia
- you, the biological father of your baby, anyone in the biological father’s family or your family, no matter how many generations back, came from anywhere in the world apart from the UK or Ireland, or
- you or the biological father of your baby does not know your family history – for example, you or the biological father of your baby were adopted.
What are the advantages of having screening for sickle cell and thalassaemia in pregnancy?
If you are a carrier of sickle cell or thalassaemia, it is important to know so you can have the right kind of care during your pregnancy. Women who know their baby has a high chance of inheriting a sickle cell disorder or thalassaemia major can have an invasive test to find out if their baby has the condition.
This could be done by either chorionic villus sampling (CVS) or amniocentesis. If your baby has the condition, you can decide whether to prepare for the birth of your baby with one of these conditions or to end your pregnancy.
What are the disadvantages of having screening for sickle cell and thalassaemia in pregnancy?
Having the test may make you anxious if you find out you carry sickle cell or thalassaemia. Some women would be offered an invasive test to see if their baby has the condition. Because the invasive tests can cause a miscarriage, many women find this a difficult decision. Some women may wish they had not had the screening test because making this decision is difficult.
Should I have the blood test for sickle cell and thalassaemia?
Only you can decide to have the test or not. Some women want to find out if their baby has sickle cell or thalassaemia, and some do not. Having the test may cause anxiety as the result may mean that you are offered further tests.
What will the results tell me?
If the result shows you are not a carrier, it is very unlikely your baby could have a sickle cell disorder or thalassaemia major. Although the test is very accurate, a small number of results may be unclear. If this happens, you will be offered another test.
If the test shows you are a carrier or a possible carrier, you will be able to talk to a specialist midwife or genetic specialist and they will give you more information.
They may suggest you ask the biological father of your baby to have a blood test to find out if he is a carrier. If his test result shows he is not a carrier, it is very unlikely your baby will have a sickle cell disorder or thalassaemia major.
If you are a carrier or have a sickle cell or thalassaemia disorder the father of your baby will be offered testing too. If the father of your baby is a carrier or has sickle cell disorder or declines testing you will be offered specialist advice on the condition and invasive testing (see section 7).
What if the biological father is also a carrier?
If the test shows the father of your baby is a carrier, there may be a 25% (one in four) chance your baby could have a sickle cell disorder or thalassaemia major. You can then decide whether to have more tests to find out if your baby has the condition.
These tests are called invasive tests (see section 7). If you choose not to have more tests, your baby can be tested at birth for sickle cell disorders or for thalassaemia major. This means that if your baby has the condition, treatment can start early.
What are the possible results from invasive tests?
If you have CVS or amniocentesis, the result may show:
- that your baby does not have this condition, or
- your baby has a sickle cell disorder or thalassaemia major. You can then decide whether to prepare for the birth of a baby with sickle cell or thalassaemia major or to end your pregnancy. CVS and amniocentesis can detect other chromosome changes. The specialist midwife or genetic counsellor will give you more information. You will be offered newborn bloodspot screening after your baby is born. This test will also look for sickle cell disorder