Thalassaemia is often detected during pregnancy or soon after birth.
Blood tests can also be carried out at any time to check for thalassaemia or see if you're a carrier of thalassaemia and are at risk of having a child with it.
Screening to check if a baby is at risk of being born with thalassaemia is offered to all pregnant women in England.
This involves having a blood test to check if you have the thalassaemia trait.
If the mother does have the trait, the father is then offered a test to see if he carries it, too.
Screening should ideally be carried out before you're 10 weeks pregnant so you and your partner have time to consider the option of further tests to find out if your baby will be born with thalassaemia.
Newborn babies are not routinely tested for thalassaemia because the test used is not always reliable soon after birth and thalassaemia is not immediately dangerous.
But the main type, beta thalassaemia major, is often picked up as part of the newborn blood spot test (heel prick).
A blood test can be carried out at any point to diagnose thalassaemia if a child or adult has symptoms of thalassaemia and the condition was not picked up earlier on.
A blood test can be done at any time to find out if you have the thalassaemia trait and are at risk of having a child with thalassaemia.
This can be particularly useful if you have a family history of the condition or your partner is known to carry thalassaemia.
If you're worried that you could be a carrier of thalassaemia, ask for a test from your GP surgery or nearest sickle cell and thalassaemia centre. Both men and women can have the test.