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How haemophilia passes through a family | CION Cancer Clinics
Haemophilia is usually passed on by a mother who carries the gene. Each of her sons has a one in two chance of having haemophilia, and each daughter has a one in two chance of being a carrier. A father with haemophilia passes it to none of his sons, but all his daughters carry it. Sometimes the gene changes new, with no family history at all. At CION Cancer Clinics, our haematologist cares for anaemia, bleeding, clotting and inherited blood disorders, with ArogyaSri, CGHS and cashless insurance accepted.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- How is haemophilia passed from a mother to her son?
- What can happen in each pregnancy?
- What if it is the father who has haemophilia?
- What do families wrongly believe about carrying haemophilia?
- Why can a boy have haemophilia when no one in the family does?
- How does a family find out who carries the gene?
- What do the genetics words mean?
- Common questions about haemophilia inheritance
The short answer
How is haemophilia passed from a mother to her son?
Haemophilia is usually passed on by a mother who carries the gene. Each son she has has a one in two chance of having haemophilia, and each daughter has a one in two chance of being a carrier like her.
Why it follows the mother's side
The genes for factor VIII and factor IX, the two clotting proteins missing in haemophilia A and B, sit on the X chromosome. A chromosome is a bundle of genes, and we get one set from each parent. Girls have two X chromosomes. Boys have one X, from their mother, and one Y, from their father.
Why sons are affected and daughters mostly are not
A boy has only one X. If that X carries the changed gene, he has no second copy to make up for it, so he has haemophilia. A girl who gets the changed gene usually has a working copy on her other X. That second copy makes enough factor for most carriers to clot well enough day to day.
The chance is the same every pregnancy
The odds do not add up or balance out. Having one affected son does not make the next son safer, and having two unaffected sons does not mean the gene has gone. Each pregnancy is a fresh chance.
This page explains the pattern. It cannot tell you whether you are a carrier. Only testing can do that.When the mother carries the gene
What can happen in each pregnancy?
This is the most common family pattern: a mother who carries the gene and a father who does not have haemophilia. There are four possible outcomes, each equally likely.
A son without haemophilia
He received his mother's working X. He does not have haemophilia and cannot pass it to his children.
A son with haemophilia
He received the X with the changed gene. His severity will usually be similar to other affected men in the same family, though not always.
A factor level test soon after birth tells you for certain.A daughter who is not a carrier
She received the working X from her mother. She cannot pass haemophilia on, and her own children are not at risk from this line.
A daughter who is a carrier
She received the changed X. She may bleed more than expected, and her own sons will face the same odds.
Worth checking in her
- Her factor level, before any surgery
- Heavy periods from the start
- Carrier status, before she plans a family
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What if it is the father who has haemophilia?
Mother is a carrier
Father has haemophilia
Each son has a one in two chance of haemophilia
No son gets haemophilia from his father
Each daughter has a one in two chance of being a carrier
Every daughter is a carrier
Carrier testing helps sort out which daughters carry it
Daughters need no test to know; they need a factor level check
The risk passes to grandsons through carrier daughters
The risk skips his sons and reaches his grandsons through his daughters
Commonly believed
What do families wrongly believe about carrying haemophilia?
"It is the mother's fault."
Nobody chooses the genes they carry or pass on. Most carrier mothers had no idea until their son was diagnosed. Blame within a family does real harm and changes nothing about the child's care.
"Carriers never have bleeding problems."
Many carriers have lower factor levels than other women. Heavy periods, long bleeding after tooth removal and heavy bleeding after childbirth are common. Some carriers have levels low enough to be treated as mild haemophilia.
"It skipped a generation, so it is gone from our family."
It often looks skipped because it passed silently through carrier women. A grandfather with haemophilia can have a grandson with it, through a daughter who never bled.
"Nobody else has it, so the mother cannot be a carrier."
She may still carry it without anyone having noticed. Or the gene change may have arisen new, in her or in her son. Only testing can tell these apart, and it matters for her sisters and daughters.
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When no one else has it
Why can a boy have haemophilia when no one in the family does?
A sizeable share of boys with haemophilia are the first in their family. There are two usual explanations, and a genetic test is the way to find out which applies.
The gene changed for the first time
Sometimes the change in the factor VIII or factor IX gene happens new, in the egg that became the child. His mother is then not a carrier, and her other children are at low risk. Doctors call this a new or de novo change.
It had been carried quietly for generations
Just as often, the mother is a carrier and so were women before her. The gene may have passed through several carrier women who never bled badly, while affected men in older generations went undiagnosed or were described simply as bleeders.
Why this question matters
The answer changes the picture for the mother's future pregnancies, and for her sisters, daughters and nieces. Testing usually starts with the affected boy, to find the exact gene change. Once that change is known, female relatives can be checked for that one change, which is simpler and clearer. Testing is usually arranged through a haematologist and a genetics service.
A normal factor level in a woman does not prove she is not a carrier. Carrier status needs a genetic test.The pathway
How does a family find out who carries the gene?
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Confirm the diagnosis in the affected boy
Factor levels confirm whether it is haemophilia A or B and how severe. Bring every past report and any treatment card.
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Find the exact gene change
A genetic test on the boy's blood looks for the change in his factor gene. This is done at specialised laboratories, and your team will tell you where the sample goes.
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Test the mother
She is checked for the same change. The result explains how it arose and guides her future pregnancies.
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Offer testing to sisters, aunts and daughters
Women on the mother's side can be checked for the same change. Each should also have her own factor level measured.
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Talk it through with a genetic counsellor
Before a pregnancy, a counsellor explains the options, including testing during pregnancy, without pressure to choose any of them.
On your report
What do the genetics words mean?
- X-linked
- A condition caused by a gene on the X chromosome. It mainly affects boys and passes through the mother's side.
- Carrier
- A woman with one changed copy of the gene and one working copy. She can pass it on and may bleed more than usual.
- Obligate carrier
- A woman who must be a carrier because of her family tree, such as every daughter of a man with haemophilia. She does not need a genetic test to know.
- De novo
- A gene change that has appeared for the first time in a family, rather than being passed down.
- Genetic counselling
- A conversation with a trained counsellor about what a test result means for you and your family, and what choices exist.
Questions we are asked
Common questions about haemophilia inheritance
My son has haemophilia. Am I definitely a carrier?
Not definitely. Many mothers of affected boys are carriers, but in some families the gene change happened new in the son. If you have more than one affected son, or an affected brother or father, you are very likely a carrier. A genetic test gives you a clear answer.
Can a girl be born with haemophilia?
It is uncommon, but it happens. It can occur when a father with haemophilia and a carrier mother have a daughter, or when a carrier's working copy is largely switched off. Some carrier girls also have factor levels low enough to be treated as mild haemophilia.
Will my husband's family history affect our children?
If your husband has haemophilia, your sons will not inherit it from him, but all your daughters will be carriers. If only his relatives have it and he does not, he cannot pass it on. The risk to your children comes through the mother's side.
Should my daughter be tested, and when?
A factor level is worth checking early, before any surgery, dental extraction or her first periods, because a low level changes how those are handled. Genetic carrier testing is often discussed when she is old enough to understand it and take part in the decision.
Can haemophilia be tested for during pregnancy?
Yes, where the family's gene change is known. Options exist during pregnancy and, for some couples, before it. Each carries its own risks and choices. A genetic counsellor and your obstetrician will explain them. What you decide is your family's choice alone.
Does a carrier mother need special care at delivery?
Yes. Tell your obstetrician early. Her factor level should be checked in later pregnancy, and the delivery planned to limit bleeding for her and to protect a baby boy who may have haemophilia. Some procedures, such as scalp clips on the baby, are usually avoided.
Can a carrier woman take part in normal life and sport?
Almost always, yes. Most carriers live without restrictions. What helps is knowing her factor level, telling doctors and dentists before procedures, and asking for help early with heavy periods rather than living with them. Some painkillers can worsen bleeding, so ask before taking new medicines.
Where can we get genetic testing done in Hyderabad?
Testing is usually arranged through a haematologist, with samples sent to specialised laboratories. CION's haematology team can review your family's reports and coordinate testing and counselling with qualified centres. Ask which laboratory is used and whether your scheme or insurance covers it.
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Sources
- NHS — Haemophilia
- NHLBI — Hemophilia
- American Society of Hematology — Hemophilia
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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