Determining Paternity

Determining paternity is now possible even before a baby is born. This is done by comparing DNA molecules -- our genetic blueprints.

Determining paternity is now possible even before a baby is born. This is done by comparing DNA molecules — our genetic blueprints.

Dr. Greene’s Answer:

Determining paternity is now possible even before a baby is born. This is done by comparing DNA molecules — our genetic blueprints. To do this you need a blood sample from both the mother and the potential father (testing without the mother’s blood is possible, but more difficult — and more expensive). You also need a small sample of amniotic fluid (the water that the baby is floating in). Less than 1/4 teaspoon is sufficient for the test. The amniotic fluid may be obtained by a process called amniocentesis. This procedure is performed no earlier than 13 weeks into the pregnancy.

A court order or informed consent of all adults involved is required to proceed with paternity testing.

You will need to wait 3 to 4 long weeks for the results. Waiting for these test results can be a very anxious time. Rush orders take 10 to 15 business days, but cost about $500 extra.

If the test says that the person tested is the father, then he probably is — there is about a 99.8% chance. DNA testing is now legally accepted in determining paternity.

Prenatal Paternity Testing

Prenatal paternity testing can be arranged through a company called Genelex, located in Seattle, Washington. They are very helpful, and can be reached at 1.800.523.6487. The test costs $700, and is usually not covered by insurance.

If you wait until after the baby is born, DNA testing can be arranged through most local blood banks (many of which use Genelex). The blood sample can be obtained at birth. Otherwise, the baby should be at least 2 months old, since a fair amount of blood is needed for the test. In my area, this option costs about $600, and is usually not covered by insurance.

HLA Typing

There is also a less expensive method. For years, the only legally acceptable way to determine paternity was something called Human Leukocyte group A antigen typing, or HLA typing, which looks at the whole complement of proteins found on the surface of white blood cells — and on most cells throughout the body. A person’s HLA type is like her genetic fingerprint. It is how her body determines if an individual cell is a part of her or an invader (a cancer, a virus-infected cell, or foreign tissue). HLA typing technology was first developed in the 1950’s to insure matching in transplant cases. HLA typing is available at blood banks, and although insurance will not cover it for determining paternity, the tests may be obtained for several hundred dollars.

Medical review by: Khanh-Van Le-Bucklin, Rebecca Hicks
Last medical review: March 03, 2008
Updated: October 1, 2020

Dr. Greene is a practicing physician, author, national and international TEDx speaker, and global health advocate. He is a graduate of Princeton University and University of California San Francisco.

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51 Comments

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  1. Diana

    Hi Doctor,

    My mother and father have blood type 0; they both are 0+ blood type. Whereas, me I have A+.
    We have recently tested and yes, my parents are 0+ , I have A+.
    Is this possible? What kind of other testing we shall perform?

    Best wishes
    Diana

    Added:
    • Cheryl Greene

      Hi Diana,

      Thanks for writing in.

      Since you’ve already retested, the next step is a DNA paternity test. You can have this done at most labs or you can do them yourself at home. Here’s one at-home DNA paternity test.

      I hope that helps.
      Best, @MsGreene
      Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

      Added:
  2. Aissa

    hi doc
    Is it possible mother is o+ and father is o+ And child a +

    Added:
    • Cheryl Greene

      Hi Alisa,

      Thanks for writing in.

      If both parents are O+ they can only have children with O+ or O- blood. They can not have a kids with A+ blood. BUT, blood types are often different than what is thought so it’s wise to have all three blood types retested before jumping to any conclusions.

      I hope that helps.
      Best, @MsGreene
      Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

      Added:
  3. Ilsa

    hi doc!
    my father is B+ mother is O+ but i am A+… how?

    Added:
    • Cheryl Greene

      Hi Lisa,

      Likely one of your blood types is different than you think. It’s wise to get all three of you retested. If the blood types come back the same, a DNA paternity test may be helpful. Or an open talk with your parents.

      I hope that helps.
      Best, @MsGreene
      Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

      Added:
  4. ZeeMass

    Both my parents are B+. I am O – and my sister is O+
    Is this possible?

    Added:
    • Cheryl Greene

      Hi ZeeMass,
      Thanks for writing in.
      Yes, this is possible. Let me know if you’d like an explanation.
      I hope that helps.
      Best, @MsGreene
      Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

      Added:
      • Zee M

        Yes please!

        Added:
        • Cheryl Greene

          B+ parent, O- writing, O+ sister

          Hi Zee,

          Blood types are comprised of two alleles. The most common (by far) are A, B, and O.
          — If a person has type B+ blood he or she has at least one B allele. He or she can have two B alleles (BB) but can also have one B and one O (BO). Both are called type B blood. That person can pass down either a B or an O to their children.

          Rh+ means a person is positive for the D antigen. Rh- means a person does not have the D antigen.
          — Two parents with Rh+ blood can have children with Rh+ or Rh- blood because they can pass down the D antigen, but do not necessarily pass it down to their children.

          What all this means is if your parents are both B+ they could have a child who is B+, B-, O+ or O- and each would be perfectly normal.

          I hope that helps.
          Best, @MsGreene
          Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

          Added:
  5. Kamal

    My ABO is B negative & My wife ABO is A Positive & Daughter’s ABO is B Positive…..is it possible?

    Added:
    • Cheryl Greene

      Hi Kamal,

      Thanks for writing in.

      Yes, it is possible for one parent to have B- blood, the other parent to have A+ blood and their child to have B+ blood. If you’d like to know how.

      Best, @MsGreene
      Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

      Added:
  6. Henry

    My Parents are o+ and A+. I was born A-. Does this add up?

    Added:
    • Cheryl Greene

      Hi Henry,

      Thanks for writing in.

      If one parent is A+ and the other is O+, it is completely normal for them to have a child that is A-. Let me know if you’d like an explanation.

      Best, @MsGreene
      Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

      Added:
  7. Sarah

    Hi Dr. Greene, to my understanding both my parents are A+ and I am O-. Is this possible?

    Added:
    • Cheryl Greene

      Hi Sarah,

      Thanks for writing in.

      Yes, it is possible for two parents who have A+ blood to have a child has O- blood. If you’d like more information, let me know.

      I hope that helps.
      Best, @MsGreene
      Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

      Added:
  8. G

    Hello Dr Greene, I am A1 positive and my husband is b positive and our daughter is b negative…Can you pls explain?

    Added:
  9. EBass

    Mother is B+ and father is O+ I am A+. Is that possible?

    Added:
    • Cheryl Greene

      EBass,

      Our current understanding of genetics is that it is not possible for one parent to be B+, the other parent to be O+ and their child to be A+.

      It is wise to have all your blood retested. It’s not uncommon for blood types to be different than they are thought.

      I hope that helps.
      Best, @MsGreene
      Note: I am the co-founder of DrGreene.com, but I am not Dr. Greene and I am not a doctor. Please keep that in mind when reading my comments and replies.

      Added:
  10. Judith Jefferys

    Hello,
    For many years I have wondered about my parents and if I was adopted.
    I am an only child and both my parents now deceased.
    Pregnant with my first child I discovered that my blood is rh o neg.
    My father is definitely A pos.
    Not sure about my mother. Trying to find out through her military records.
    Is there a specific blood she would need to be for me to be rh o neg?

    Added:
    • Cheryl Greene

      Judith,

      If your father was A+ and if you are O-, your mother could be A+, A-, B+, B-, O+ or O-. She could not be AB+ or AB-.

      Best, @MsGreene
      Note: I answer a lot of questions on DrGreene.com, I am the co-founder of DrGreene.com, Dr. Greene’s business partner, but I am a not doctor. Please keep that in mind when reading my comments and replies.

      Added:
  11. Shane

    Hi both my parents are a+ I am b- what are the chances one of them aren’t my biological parents

    Added:
    • Cheryl Greene

      Shane,

      Our current understanding of science is it is not possible for two A+ parents to have a child that is B-.

      It is wise to have all your blood retested. It’s not uncommon for blood types to be different than they are remembered.

      @MsGreene
      Co-founder & Executive Producer DrGreene.com, Mom

      Added:
  12. Pam

    Can a AB postive man have a AB positive child. Not sure of moms blood type

    Added:
    • Cheryl Greene

      Pam,

      If one parent is AB+, he or she can have a child who is AB+ if the other parent is A+, A-, B+, B-, AB+ or AB-, but not if the other parent is O+ or O-.

      Best,
      @MsGreene
      Co-founder & Executive Producer DrGreene.com, Mom

      Added:
  13. Michelle

    Mother is type O+ and baby is type B+. Father is type O+(found out after a year later). After reading about A/B/O blood types and possibilties, my child fell into the impossible blood type list. With few exceptions in very rare cases, sometimes that will happen or so I read. My child has the Delta-Beta Thalassemia Trait. Could this have changed his blood type? I have the Alpha Thalassemia Trait. Father not involved in our lives. Please advise. Thank you.

    Added:
  14. Jeanne

    Can parents, blood type A negative and B negative, have a child A positive blood group?

    Please tell me.

    Added:
    • Cheryl Greene

      This is not considered a possible outcome. Please consider having everyone retested before jumping to any conclusions.

      Best,
      @MsGreene

      Added:
  15. Dawnella

    My mother is rh o neg ,Iam also.Is my father supposed to be rh also?

    Added:
  16. ij

    Hi! I have a daughter who happens to be O positive. But my husband’s blood type is Type A+ while I am O+. Upon reading, it says that Type A blood type is always dominant with Type O. Is this possible?. Please advise.

    Added:
  17. John allah

    I am O+ and my daughter is O+. Does this in any way associate both of us DNAs for paternity? Can you comment please?

    Added:
    • Cheryl Greene

      This does not determine paternity, but it is a possible outcome, i.e. it does not rule you out as the father. DNA testing is needed to determine paternity.

      Hope that helps,
      @MsGreene
      Executive Producer, DrGreene.com, citizen scientist, mother

      Added:
  18. Andrea

    Can both parents blood type 0 plus have a baby with Bloom type 0 rh negative?

    Added:
  19. Adrian

    My ex wife blood group is a+ , mine is B+ our duaghter is O+ what is the percentage that I am my daughters biological father?

    Added:
    • Cheryl Greene

      According to what we know about genetics now, there is a 6.25% chance each child of parents where one is A+ and the other is B+, will have O blood type and a 93% chance the child’s blood will be Rh+.

      Added:
  20. Lori Pequeno

    My mother and father are deceased. I believe my mother was ab+ and my father was o- or rh-. My mother kept me away from my father. My aunt and uncle practically raised me. I found out my blood type is b-.
    Was my father my father?

    Added:
    • Cheryl Greene

      It’s not possible to know for sure based on blood types alone, but this is a possible combination. In other words, your blood types do not give you any reason to believe he is not your father.

      Added:
    • Dwight pryce

      if my mother blood type is B and my Father is a what mine should be

      Added:
      • Cheryl Greene

        Hey Dwight,

        Your father’s blood type didn’t come through. What is it?

        @MsGreene

        Added:
  21. Yvonne

    According to my mother, both she and my father are 0. All my sibling are 0. I, however, am A+. Does it mean there is a problem with regards to them being my biological parents? My mother swears she was only ever with my father.

    Added:
    • Cheryl Greene

      Two O blood type parents can only have an O blood type child, but often people are mistaken about their blood type. Before you jump to conclusions, you should all be tested again to confirm.

      Added:
  22. angela

    can two parents who are o positive blood type have an o positive child?

    Added:
    • Cheryl Greene

      There is a 93.75% chance that two parents with O+ blood will have a child with O+ blood type.

      Added:
  23. Halle

    No one in my family has my blood type. My blood type is O Negative. Is that common or does it mean I am not biologically related to my family.

    Added:
  24. Halle

    What does it mean if no one in your family has your blood type. My blood type is O Negative. Is that common or does it mean I am not biologically related to my family.

    Added:
  25. liz

    Can a mother with blood type A and AB father have an O blood child?

    Added:
  26. Anup Solanki

    Can parents, both blood type o positive, have a child B negative blood group?

    Please tell me.

    Added:
  27. jenifer

    Is it possible for a baby to be AB positive while one parent is A negative and other is O positive?

    Added:
  28. Sue

    Can a ‘paternity’ test be done on adult children, when one parent has already deceased? I mean, would I be able to use my Uncle’s blood sample (if he were willing), in place of my Dad’s?

    Added:
  29. Elaine

    Since Eva was a clone of Adam’s DNA, having his exact same flesh and bone; and blood is manufactured in the bone, how could the three different blood types have evolved? Seems to me it would be a closed repeating loop.

    Added:
    • Aladdin

      You are right and the result is eve is not from adams flush she is from heven and each son of adam get a wife from heven becouase its impossible to have brothers marry his sisster in the laws if god and geneticly

      Added:

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