Hemophilia is an inherited bleeding disorder. This means it’s passed down in genes. People who carry the genetic information but do not have the disorder can still pass the gene to their children.

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Hemophilia is a bleeding disorder in which your blood does not clot as it should. This disorder is genetically inherited, which means it’s passed down in families. If a person inherits the affected genes, they can either have the disorder or be considered a carrier.

Here’s more about what it means to be a hemophilia carrier, who is more likely to be one, and what tests can help you learn your carrier status.

Learn more about hemophilia.

A hemophilia carrier is a person who carries the genes for hemophilia (Factor VIII or Factor IX). Only females can be carriers because the genes for hemophilia are carried on the X chromosome.

Females have two X chromosomes. If one of those chromosomes is affected, the other may make up for it and provide the needed clotting factors in the blood. Therefore, a female can have the genetic information for hemophilia but not have the disorder.

Males, on the other hand, have just one X chromosome. If it’s affected, there is no backup, and the person will have hemophilia.

Language matters

In this article, we use the terms “male” and “female” to refer to someone’s sex as determined by their chromosomes and not to their gender.

The research cited uses the terms “male,” “father,” and “son” to indicate individuals with XY chromosomes and the terms “female,” “mother,” and “daughter,” to indicate individuals with XX chromosomes, and the genetic causes of hemophilia are directly related to the X chromosome.

A person’s gender identity may differ from the sex they were assigned at birth.

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Your doctor can order blood tests to find out your carrier status.

A clotting factor test — factor assay — is 80–90% accurate in determining whether someone is a carrier. But factors such as pregnancy, nursing, and taking birth control pills can affect the results of this test.

Genetic (DNA) testing is another option. This type of test involves examining a blood sample to look for specific genes that cause hemophilia. A family history of hemophilia is another factor doctors consider in interpreting the test results. Genetic testing is nearly 100% accurate in determining carrier status.

How is carrier screening done?

Screening tests are performed by taking a blood sample. Your doctor will order a blood test in a lab. After giving your blood sample, you’ll wait up to 3 months for the results. You may get your results sooner if you’re pregnant.

What do carrier screening results mean?

If your result comes back positive, it means you carry the genetic information for hemophilia on one of your X chromosomes. This means you can pass the gene to your children.

If your results show that you’re a carrier, you can talk with your doctor about the details.

According to the Centers for Disease Control and Prevention (CDC), your level of clotting factor determines your carrier status:

  • A clotting factor level of less than 40% means you have mild, moderate, or severe hemophilia.
  • If you have a clotting factor level of 40% or more and you have bleeding symptoms, you’re a symptomatic carrier.
  • If you have a clotting factor level of 40% or more without bleeding symptoms, you’re an asymptomatic carrier.

You’re likely to be a carrier of hemophilia if you’re female and:

  • your biological father has hemophilia
  • you have more than one child with hemophilia
  • you have a child with hemophilia and another blood relative with hemophilia

Otherwise, you might want to consider screening if:

  • you have bleeding symptoms
  • hemophilia runs in your biological family
  • you have a male partner with hemophilia and you want to have children together

You may choose to undergo carrier screening at any time.

However, some people decide to get screened before pregnancy. Testing at this time can help you understand what being a carrier means and what the implications are for your future children.

A father who is a carrier cannot pass the affected X chromosome to their male children because the male children inherit the Y chromosome. But all female children of a father who is a carrier will also be carriers because they’ll inherit the affected (and only) X chromosome from their father.

Each male child has a chance of inheriting their mother’s affected X chromosome, which would cause hemophilia. Likewise, female children — who inherit an affected X chromosome from their father 100% of the time — might also inherit the affected X chromosome from the mother. If a female child inherits two affected X chromosomes, they will have hemophilia.

A genetic counselor can help you evaluate your chances of having a child with hemophilia.

People with hemophilia can live long, relatively healthy lives. Treatment involves replacing the clotting factors that are missing. This can be done after an acute injury (to stop active bleeding) or prophylactically (to prevent bleeding).

Continued treatment by doctors familiar with the disorder is key. Some older research suggests that hospitalization and mortality rates for bleeding are 40% lower in people who receive treatment in hemophilia treatment centers than in those who do not seek this specialized care.

Without treatment, people with hemophilia may develop joint disease, heart disease, or kidney disease.

Do hemophilia carriers have symptoms?

A carrier may be asymptomatic (showing no symptoms) or symptomatic (with symptoms). In some, the other X chromosome can provide enough clotting factor so that bleeding isn’t an issue. In other cases, a carrier may have some bleeding issues.

Why can only females be carriers of hemophilia?

Females can carry hemophilia because they have two X chromosomes. If the clotting factors on one X chromosome are affected, the other X chromosome may make up for it.

Males have one X chromosome and one Y chromosome, which does not have clotting factors. So, if the X chromosome is affected, the person will have hemophilia.

Can a hemophilia carrier have a baby?

Yes. A female who is a carrier of hemophilia can have a baby. Genetic testing of both parents can help determine the chances of passing the disorder to children.

A simple blood test can help you find out whether you carry the gene for hemophilia. Carriers can have symptoms in some cases, and you can speak with your doctor about any necessary treatment or precautions you should take to avoid excess bleeding.

Your doctor can refer you to a genetic counselor to discuss how your carrier status may affect your future children.