Haemophilia is quite a rare condition, with about 1 in 10,000 people is born with haemophilia A and about 1 in 50,000 people is born with haemophilia B. Haemophilia is an X-linked recessive disorder (males have the condition and females are usually only carriers ). The condition can be passed to a child by either one or both of their parents. A man with haemophilia will have sons that are unaffected by haemophilia, but all his daughters will be carriers. A female carrier has a 25 per cent (1 in 4) chance of having an affected son and a 25 per cent (1 in 4) chance of having a carrier daughter for every pregnancy. There's also the chance that a girl could be born with haemophilia if both parents have the haemophilia gene. Unlike haemophilia, von Willebrand disease (vW), affects males and females equally, but women may also experience gynaecological problems linked to vW.
Approximately two thirds of all children born with haemophilia will have a known family member who has, or has had, haemophilia. The remaining third will have new spontaneous genetic mutations that are responsible for the condition. This new mutation may be either in the child or in their mother, who may then have subsequent children who are affected by haemophilia.
If there is a family history of haemophilia, tests are available on the NHS before, during and after pregnancy to discover if you or your child is a carrier or has the condition. If there's no family history, haemophilia is usually only diagnosed when symptoms, such as joint bleeds or easy bruising, appear in childhood. Mild haemophilia may only be discovered after an injury or medical procedure. A blood test can distinguish between haemophilia A or B.