Haemophilia is usually inherited. This means that it passes down from one generation of a family to the next in their genes. For females to have severe haemophilia, they must have two copies of the faulty gene – one on the X chromosome inherited from their father and one on the X chromosome inherited from their mother. This is very rare.
More commonly, females have one faulty copy of the gene and one normal copy. They are known as 'carriers' and usually have enough clotting factors from their one normal X chromosome to prevent serious bleeding issues. However, up to 50 percent of carriers may have an increased risk of bleeding.
When a carrier mother and a father without haemophilia have a daughter, she will have a 50 per cent chance of inheriting the faulty gene from her mother and being a carrier. So if you are a carrier yourself, you will need to ensure that your daughter undergoes testing at some point to determine whether she is also a carrier. If you are thinking about having another child at this stage, you can find more information here.
When should carrier testing be done?
There is no ‘correct age’ to test a woman’s hemophilia carrier status and it really depends on what you and your family feel comfortable with. In some cases, families choose to delay testing, while others prefer to test a child who may be a carrier early on, so that any necessary precautions can be taken. In general, females are usually tested for carrier status some time after they start menstruating, when they are old enough to make an informed decision.
Here are a few things to consider that might help you make your decision:
- If your daughter requires a planned surgical procedure, medical professionals recommend that possible carriers get their clotting factor levels tested so that they are well prepared to manage any bleeding risks that may arise during the procedure.
- If your daughter seems to have a bleeding tendency, for example bruising easily or heavy menstrual bleeding, it may be a good idea for her to undergo genetic testing. This way, if she is a carrier and has lower than normal blood clotting factor levels, you can take any necessary precautions.
- Testing prior to pregnancy is a good idea for three main reasons
- Firstly, clotting factor levels rise during pregnancy, making test results unreliable and the results of genetic testing may not be available for weeks.
- Secondly, your daughter may want to undergo genetic counselling with her partner so that they fully understand the options available to them if she is a carrier. Genetic counselors are trained in both human genetics and counselling so are a great resource when discussing the pros and cons of different options for starting a family.
- Thirdly, labour and delivery pose potential threats to babies with haemophilia, because of the trauma related to the birthing process. As a result, hospital staff must be prepared to provide appropriate treatment to the mother and child.
Ultimately, deciding when your daughter undergoes genetic testing to determine whether she is a carrier of the haemophilia gene is a decision that is best discussed with your healthcare professional. Your Haemophilia Treatment Centre can help you weigh up the pros and cons of each option to help ensure that you are comfortable with your decision.