Determining Paternity

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

Question

What kind of test is done to determine who a child’s father is?

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.

Last medical review on: March 02, 2008
About the Author
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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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Recent Comments

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.

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

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.

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.

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

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.

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.

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

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.

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.

Yes please!

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.

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.

Yes please!

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

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.