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Genealogy Research

7 Steps for Using DNA to Find Birth Parents of Adoptees & Others with Unknown Parents

Trying to find birth parents? DNA and genetic genealogy along with good detective work and plain old fashioned genealogy research can yield results.

I am thrilled to have Mary Eberle, JD of DNA Hunters  as a guest writer today! Welcome, Mary!

Many adoptees and others looking with unknown parents use DNA in their searches. There are techniques and resources for this work that can be broken down into 7 steps, which are discussed below.  

Before jumping into DNA, it’s important to consider what non-DNA resources might help in searching for a birth parent.

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Non-DNA Resources To Find Birth Parents

Original Birth Certificates 

State laws govern adoptees’ rights to access to their original birth certificate (OBC), which are created at birth and should list one or both birth parents. It’s important to check for the current law, because states occasionally amend their laws to allow access.  A quick google search is the easiest way to do this. 

In states that allow adoptees to access their OBCs, usually children of a deceased adoptees can also access a parent’s OBCs after proving they are the adoptee’s child.  

Obtaining an OBC can answer all questions in some cases. However, sometimes a birth father (BF) is listed as “father unknown.”  In other cases, some information on the OBC is incorrect, or the entire OBC is incorrect.  This was common back before women had to provide ID at delivery.  In some of these cases, the adoptive families’ names were put on OBCs.

Closeup detail of birth certificate form to be filled out when baby is born

DNA can be used to know whether an OBC is correct in most instances.  Therefore, just because you find an OBC, the search doesn’t need to stop there.  Instead, DNA can be used to confirm the birth parents listed on an OBC.

Adoptees’ Non-identifying Information

Non-identifying information (NII) is information usually collected by an adoption agency. It includes things like the birth mother’s age, religion, education, and her family composition. Some information is provided, but not enough to identify the birth parents. 

It’s important to try to obtain an adoptee’s NII. But, like with original birth certificates, NIIs aren’t always accurate. For example, if it was easier to find adoptive parents for Jewish children, a Catholic child might be recorded as having Jewish birth parents.

Although NIIs aren’t always accurate, there may be kernels of truth in them.  For example, maybe the birth mother’s first name is correct, but her last name isn’t.  Try to keep this information in mind as further research, such as DNA research, is being conducted.  

Others with Unknown Parents (OWUP)

In addition to adoptees, others might have unknown parents.  They include those who are donor-conceived, ones who find through a DNA test that a “not the parent expected” (NPE) event has occurred in their lineage, and people who never knew who their birth father was.  OWUP typically won’t have an original birth certificate or non-identifying information that can help their search.  Instead, they can rely on DNA and family stories.

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The DNA Work To Find Birth Parents

DNA Steps

This is often an iterative process with the steps below repeated.

  1. Test adoptee (or other person with unknown parents) and others
  2. Create genetic networks (GNs)
  3. Predict matches’ relationships
  4. Review trees for common ancestors
  5. Build trees back & then forward
  6. Develop & test hypotheses
  7. Reach out to birth family

The 7 Steps in Detail

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Step 1 – Test Adoptee and Others

A. Testing Autosomal DNA

The adoptee or other person with unknown parents should have their autosomal DNA tested.  AncestryDNA is a good place to start because its database is the largest.  It also has useful tools, and many people have family trees associated with their DNA results. Oftentimes, testing at Ancestry alone will find a birth parent.  However, other times, the person will need to test at or transfer to other DNA companies and use GEDMatch.com.   The other places to test autosomal DNA include 23andMe, FamilyTreeDNA, and MyHeritage.

Testing Other’s Autosomal DNA

Testing ½-Siblings – Testing others oftentimes helps in the search.  For example, testing a ½-sibling can be useful.  Each DNA testing company has a “shared match” feature that finds DNA matches common to the tester and one of their matches.  In the case of a ½-sibling, their shared matches can be used to help identify their shared birth parent.  If that’s not the person being sought, those shared matches can be eliminated from further analysis.  Let’s say there are ½-siblings sharing their birth mother.  The tester is looking for her birth father.  Then all of the shared matches with her maternal ½-sibling can be ignored.  This leaves a pool of matches that’s enriched for paternal matches. There are limits to using shared matches that start at the 3rd cousin level.  This means that if a 3rd cousin match isn’t shared by both ½-siblings, it could come from either side of the family.  For a table showing the probability of various cousins matching, see https://isogg.org/wiki/Cousin_statistics.

There are a couple of other nifty techniques that can be used for specific situations. 

  • Where two ½-sisters share a birth father, they will share an entire X-chromosome.  This is relevant for 2 adoptees who are ½-sisters, but they don’t know if they share a mother or father. 
  • If two ½-brothers share a birth father, they’ll share their Y-DNA.  This is relevant for 2 adoptees who are ½-brothers, but they don’t know if they share a mother or father.
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 Testing Birth Mothers – Where a birth father is being sought, a birth mother’s test results will help filter DNA matches into maternal and paternal matches.  If a mother isn’t available, maternal relatives can be used to partially filter matches.

Testing Offspring of a Deceased Adoptee – If the adoptee is deceased, their living children can test. If not, then grandchildren can test. Finding an adoptee’s birth parent is easier if the adoptee can test. However, it is possible to do with their descendants’ DNA tests.

B. Testing Y-DNA

Testing Y-DNA can help males looking for a birth father or their father’s father.  It can also be helpful farther back in time, but it only helps on this direct paternal line.

The least expensive way to examine Y-DNA is to test with 23andMe, as they include a Y-haplogroup with their autosomal DNA test.  This might help two ½-brothers possibly sharing a birth father.

In addition, FamilyTreeDNA (FTDNA) does Y-DNA testing.  FTDNA provides a Y-DNA haplogroup and a match list. One can start with a Y-37 test (37 Y-DNA markers), which can be upgraded to more markers, e.g., Y-111. However, matches sharing a single surname occurs only 30-40% of the time with Y-37.  For example, all matches are Mr. West, and their oldest known ancestor is Mr. West.  

Instead, it’s twice as likely that multiple surnames appear.  In addition, some men get no Y-DNA matches. Getting a single surname can be immensely helpful. However, multiple surnames usually don’t help—unless there’s a shared geographic location for the matches.

C. Testing mitochondrial DNA

Testing mitochondrial DNA (mtDNA) can help for anyone looking for a birth mother or their mother’s mother.  It can also be helpful farther back in time, but it will only help on this direct maternal line.

The least expensive way to examine mtDNA is to test with 23andMe, as they include a mt-haplogroup with their autosomal DNA test.  This would be a good way to go for two ½-siblings possibly sharing a birth father.

In addition, FamilyTreeDNA (FTDNA) does mtDNA testing.  FTDNA provides a mtDNA haplogroup and a match list.

However, mtDNA rarely provides helpful information for birth parent searching.

Step 2 – Create Genetic Networks (GNs)

A GN is a group of shared matches who are related to each other. They share multiple DNA segments passed down from one or more common ancestor.  

Shared matches, which are matches who match you and one or more other match, are called different things at the DNA testing companies.

  • Ancestry.com: Shared Matches
  • FamilyTreeDNA: In-Common With
  • 23andMe: relatives in common
  • My Heritage: Shared DNA matches

Ancestry now has a color-coding system for matches that is useful for color-coding GNs.

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Step 3 – Predict Matches’ Relationships

Next, predict the matches’ relationships to the adoptee (or other person with unknown parents) based on the amount of shared DNA.  In general, the more shared DNA, the closer the relationship is. However, starting around the 3rd cousin level, the amount of shared DNA various tremendously.

DNA sharing can be measure in centimorgans (cMs) or percents. A centimorgan (cM) is a measurement of DNA.

DNA testing companies don’t always correctly predict relationships.  We see the following.

  • Ancestry – underestimates (says relationship is more distant) 
  • FamilyTreeDNA – overestimates (says relationship is closer)
  • 23andMe – most accurate, but doesn’t always list all possibilities

You should do determine possible relationships yourself.  A tool for this is the Shared cM Project Tool at https://dnapainter.com/tools/sharedcmv4.  It converts amount of shared DNA into possible relationships, along with their probabilities.

Step 4 – Review Trees of the GN for Common Ancestors

Review the trees of the various genetic networks (GNs) for common ancestors, locations, or ethnicities for people in the GN.  Sometimes just a surname is initially identified.

In the trees, consider the most likely relationships.  This tells you where in the matches tree to look in terms of grandparent, great grandparent, etc.

Oftentimes, trees of matches must be built or extended.  This can be done in an experimental tree on Ancestry that’s both private and unsearchable.  Ideally, all of the trees of the GN are combined into one tree.  The tree’s branches might not initially be connected, but eventually at least some of them should connect.

The word MYSTERY written in vintage lead letterpress type

Step 5 – Build Trees Backward and Forward

What’s different about adoption/unknown parentage work is that trees of GNs are built back in time to find common ancestors of the GN and possibly further back. How far back is based on the closeness of the relationships of the adoptee or other person with unknown parents to the matches. 

Trees are then built forward in time to the relevant time period to find the right person in the right place. 

Trees Intersecting: Oftentimes two different GNs’ trees intersect to produce the birth parent. For example, the adoptee tests and has Jones cousins in 1 GN and Smith cousins in another. The Jones tree and a Smith tree should unite to produce a birth parent—or one of their parents. Bringing the trees forward in time (hopefully) produces this union.

Step 6 – Develop & Test Hypotheses

The next step comes once a potential birth parent or set of possible ones are found.  For example, from the GN tree building, a set of brothers or cousins that might be the birth parent is identified.  Now, these possibilities should be tested and refined. 

The What Are the Odds Tool (WATO) at https://dnapainter.com/tools/probability analyzes how someone fits into a GN’s family tree. That someone might be an adoptee, an adoptee’s child or grandchild.  A tree is built in WATO that includes the possible birth parents and their shared ancestors.  Next, the different places that the adoptee (or other person with unknown parents) could fit into the GN’s tree are added as “hypotheses.”  For example, WATO can analyze the following hypotheses. 

  • Hypothesis 1 is s/he is the child of Brother 1
  • Hypothesis 2 is s/he is the child of Brother 2
  • Hypothesis 3 is s/he is the child of Cousin 1

WATO uses the shared amount of DNA from multiple matches in the GN to test these hypotheses.  WATO calculates the probabilities that the various hypotheses are true.

WATO can be used to identify additional people to DNA test, such as a possible ½-sibling. 

Step 7 – Reach out to Birth Family

After running the WATO tool, it’s time to reach out to the birth family—if this is desired.  There are good resources for this, including a form letter, Letter to a Birth Parent, at https://thednageek.com/letter-to-a-birth-parent/

There is also a new book that includes sample language for reaching out to birth families.  It also discusses possible reactions of a birth family.  It’s “The DNA Guide for Adoptees: How to use genealogy and genetics to uncover your roots, connect with your biological family, and better understand your medical history” by Brianne Kirkpatrick and Shannon Combs-Bennett.  



Using DNA to find birth parents relies on having good matches with good trees.  It also relies on detective work and genealogy records.  Some searches are very straightforward, taking only a few hours.  Others take months or year—or go unsolved at least for now.


If you’d like help with your search, author, Mary Eberle, is available.


Mary Eberle, JD founded DNA Hunters in 2015 after careers as a biotech patent attorney and scientist.  She uses the power of DNA to find birth parents of adoptees and others with unknown parents and grandparents.  She solves family mysteries by analyzing DNA test results and genealogy records.  Mary explains DNA results to clients with clarity, simplicity, and compassion.  In her free time, she loves traveling and camping with her husband in their tiny RV. Find Mary at:

Website:  https://dnahunters.com
Facebook:  https://www.facebook.com/DNAHunters
LinkedIn:  https://www.linkedin.com/in/mary-eberle-jd
Instagram:  https://www.instagram.com/dna_hunters 

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  • Emily D Aulicino


    I wanted to thank you for all they great blogs you are doing. AND, to double thank you for using the term I coined sometime prior to my book which was published in 2013. I should have stated it was me in the book, but I wasn’t thinking. The term is the revision of NPE. We in the genetic genealogy field said Non Parental Event, but I feel that every birth is a parental event! LOL..You do not have to be married to be a parent! So, I coined the term Not the Parent Expected.

    I appreciate you using it.

    Another “focus” (i.e, rant) is to stop using the term Ethnicity as that is a social construct not a scientific one. I wish the companies would just stop that. We can educate the public if we want to do so and so can they. It should be Admixture (a mixture of your biological ancestors’ population groups) or the term bio-geographical population comparison or regional comparison.

    Thank you again!

  • Mary Eberle

    Thanks, Emily, for your comment on what NPE stands for. I didn’t realize that you had coined the much better version of that term.
    I have to admit using the term ethnicity when I’m talking genealogy. I wish the genealogy community would adopt the term admixture instead. I’m going to start making an effort to do so!

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