Posted by & filed under Chimerism, Paternity Testing, Vibrant Gene.


You may have seen a CSI drama where a man is exonerated from a crime he actually committed because he has two different genomes (sets of DNA).  At the scene of the crime, he leaves traces of the alternate genome behind.  The lab tests the alternate genome, which doesn’t match the DNA in his blood.  He is erroneously declared innocent.  This might sound like science fiction, but this genetic condition is real and it silently impacts the lives of everyday people.  

What is chimerism?

The term chimera is derived from a Greek mythological creature that was composed of a goat, a lion, and a snake.  Although this monster never existed beyond our collective imagination, the health condition is quite real.  Chimerism is a condition whereby a person has not one but two complete genomes (sets of DNA) in their body.  One genome is found in one region or organ(s), while the other genome can be predominant in other organs or tissues.  So a DNA test result would be entirely different depending on where the sample was originally from (blood, saliva, fingernail clippings or hair, etc).  As you can imagine, this condition can lead to confusing results when the person seeks medical care or relationship testing!


One young chimeric father I know reported being sent to a hospital after a car accident.  When the hospital staff discovered he has two different, incompatible blood types flowing through his veins, they asked if he had received a bone marrow transplant.  Hospitals are usually ill-equipped to identify and treat chimeric individuals.



One mother’s story

Perhaps the most famous example of a human chimera is Lydia Fairchild.  Lydia applied for child support for her two children after separating from her husband in 2002.  At the time, she was pregnant with their third child.  She was required to prove a biological relationship to the kids, so she submitted DNA samples for routine DNA relationship testing.  Her husband was confirmed as their biological father, but the test indicated she was not the mother.


How could this be possible?  Lydia conceived both of her kids naturally, carried them to term, gave birth, and was being told she was not their mother.  Without knowledge of her condition, Lydia was accused of fraud. She nearly lost her two children to child protective services.


Lydia was court ordered to have a witness present at the birth of her third child to take a DNA sample immediately following the birth.  Again, the third child’s DNA test excluded her from being the mother.  Thankfully, a geneticist thought to test her cervical cells’ DNA, and indeed that DNA matched her son’s genome.  In essence, Lydia had delivered a child from her twin, thereby becoming both the child’s mother and biological aunt. Take a moment to let that sink in.


What causes chimerism? 

There are many types of chimerism, and various root causes.  For the type of chimerism mentioned in this blogpost (also known as ‘tetragametic’ chimerism), the most common cause is a twin pregnancy that naturally reduces to a single baby.  This is referred to “vanishing twin syndrome” because one embryo doesn’t survive and the embryo’s cells are absorbed by its twin and the mother.  The remaining embryo incorporates the disappearing (“ghost”) twin’s cells into various tissues and develops to a healthy baby.


Back to Lydia Fairchild, and her story.  What most likely happened is Lydia absorbed cells from her fraternal (non-identical) twin while still in utero.  Her twin did not survive to term and all that remained of the embryo were the cells that Lydia retained in her ovaries and other organs.  Lydia’s blood had her dominant genome. So when social services took a blood sample for routine maternity DNA testing, it did not match her child’s genome.



Lydia unknowingly passed on her second genome to her baby.  In doing so, Lydia became the child’s mother and simultaneously, the biological aunt.    


An even more common form of chimerism is called microchimerism.  Microchimerism is defined by a person harboring a small percentage of cells that originate from another individual.  Frequently, this condition arises during pregnancy when a mother and the fetus exchange cells across the placenta.  Microchimerism has been detected in women who have never had a full-term pregnancy, but may have been unknowingly pregnant and miscarried.  A transient form of microchimerism can also occur after a blood transfusion or organ transplantation.  The baby’s stem cells may be acting to help protect the mother from her own autoimmune condition. For reasons not fully understood, many mothers report relief from rheumatoid arthritis during pregnancy. There is reason to believe that microchimerism may be the underlying explanation.



How does a person learn that they have chimerism? 

Most chimeras are believed to be asymptomatic and completely unaware of their condition.  Medical literature has identified some common symptoms including having different colored eyes, patches of different skin tones, different colored sections of hair, and, sometimes, disorders of sexual differentiation (formerly called hermaphroditism).  Some chimeras have autoimmune diseases because the body recognizes the twin’s genome as a foreign substance.  This does not suggest that anyone who has different colored eyes or skin, or an autoimmune condition has chimerism.



How common is chimerism?  The answer might surprise you…

To understand how frequent chimerism might be, we first need to understand some things about twin pregnancies.  A surprising number of single babies were originally twin pregnancies, where the twin did not survive to term.  An estimated one in eight (or 12%) babies born had a twin that disappeared, and left no evidence of their existence.


Unfortunately, we don’t have enough scientific evidence to make an accurate prediction for the rate of chimerism in humans.  Currently, there is no public-wide screening program in the US, nor is there any real need for it since most chimeras are healthy folk.  We do know that, through the popularity of assisted reproductive technologies (such as IVF), twinning is on the rise, and we can anticipate chimerism to become more common.  Microchimerism is believed to be the most common form of chimerism, with an estimated 20-90% of women harboring cells from prior pregnancies.  The rate of microchimerism in men is less well known but assumed to be the same as women.



What increases the likelihood of chimerism?

Anything that increases the likelihood of a twin pregnancy increases the chances of a person being an undiagnosed chimera.  If your parents utilized assisted reproductive technologies, such as IVF or used fertility medications, your chances of having been a twin pregnancy are more likely.  Left-handedness has been observed more frequently in twins, leading some experts to believe that a left-handed individual may be more likely to have had a twin in utero.



What can I do if I suspect I have chimerism?

Chimeric individuals usually live healthy, normal lives–until something goes wrong involving DNA testing.  If you have had a parental DNA test performed, and the result was (falsely) negative, chimerism may be an explanation.

Contact us at for additional information.  We have a proven track record for successfully identifying chimeric individuals through cutting-edged DNA testing, and advocating for parental rights.




31 Responses to “Giving Birth to Your Sibling’s Baby: The Intriguing Condition of Chimerism”

  1. Karen

    My husband has two different colored eyes. When younger he was always told he had blood type AB when giving blood and medical procedures. Recently previous to s surgery he was told that his blood type was A.
    His mom was given blood transfusions while pregnant with him. Any connection?

    • Kayla Sheets

      Hi Karen,
      Your husband seems to have two traits that are suggestive of chimerism. If that is the case, his condition would have arisen while he was developing in utero, much like Lydia Fairchild. His mother’s blood transfusion would not have impacted his blood type. Hope this helps! If you have children, be wary of any paternity or ancestry testing because both could give you misinformation!

  2. Amanda

    When my daughter gets a suntan she has a defined line down the middle of her stomach of different skin tones. The doctor was so baffled when he saw it he asked another person to come in and look at her belly. He said it was most likely just different pigments to her skin. I wonder if that’s true after reading this.

  3. Marcus

    This is really an eye opening topic. This might explain why we can’t really jump into conclusion right away during maternal and paternity testing. This could be damaging if we just rely on single testing. Jeremy Kyle need to watch out!!

    • Kayla Sheets

      Hi Marcus,
      You are absolutely correct. If a parent has chimerism, and they’re unaware of their condition, they won’t know that the paternity test is failing them. This is a very tricky situation, and i recommend you contact a genetic specialist to get advice. At Vibrant Gene, we are regularly contacted by folks who are certain the DNA test is incorrect, and we provide private investigator services for them.

      • Twolip

        Every since I originally saw Ms. Fairchild’s story a while back I’ve always questioned DNA test on Paternity Court where the child looks exactly like the suspected father. This is a wild topic that many don’t consider or even know about. WOW!!!!

        • Kayla Sheets

          Hi Ammita,

          We have similar hesitations about paternity tests when they are negative, but the mother is certain that the father is the biological father. Chimerism is considered to be rare, but it has been proven to confound these results in surprising ways. It always pays to get a second opinion on these test results, and sometimes follow up with alternative (more robust) testing!

          Thanks for your insightful comment!
          Kayla and crew

  4. Smith

    I donated blood at 22, and found out I was A+. This ultimately led to me discovering I was born with the assistance of IVF. At 25, I had my blood tested before he birth of my 1st son, and it showed my blood type was O+. I have discovered who my sperm donor was through Ancestry, and a lot of sleuthing. I’m thankful the original test was able to enlighten me on the truth of my biological origins, but now I’m confused why the blood test during pregnancy showed something different…

  5. Brandon

    So I am aware that my twin ‘died’ but my mom said that she was having difficulty with growing what chance would this be of me having 2 strands of DNA?

    • Kayla Sheets

      Hi Brandon,
      It sounds like you were originally a fraternal twin pregnancy, and with a demise, it is not impossible that you have tetragametic chimerism. If you are interested in learning about DNA testing, feel free to contact us.

  6. Theresa Julius

    My son may have this. My son was born with multiple double anomalies. At 5 months gestation, he was thought to be a hermaphrodite bc he had what looked to be a urethra track of a male and the labia of a female. An amniocentesis was performed and showed he had the xy chromosome of a male. When he was born, he had hydrocephalus, white brain matter damage, ambiguous genitalia, duplicate right kidney, hypospadious (2 urethra), a 13th lumbar vertebrae (you are only born with 12 typically), and an imperforated rectum. The geneticists also noted that he had a 3rd and 4th nipple. It wasn’t discovered until he was almost a year old that he had 2 different eye colors. The geneticists stated that he was supposed to be a twin in early utero and that the twin’s embryo didn’t survive for whatever reason and Christian absorbed the embryo, causing multiple double anomalies. Could this be a form of chimera?

    • Kayla Sheets

      Hi Theresa,
      Based on your description of your son’s condition (in particular, his genitalia, and two different eye colors) chimerism is quite possible. Does he have patches of two-toned skin or hair of different colors/textures? It can be extremely challenging to isolate the alternate genome, and part of that challenge is just getting enough tissue samples. Feel free to message us privately if you’d like more information. Best wishes to you and to your son.

      Kayla Sheets,

  7. Nelly

    Very interesting. My son has a defined line down his abdomen and one side is darker than the other. He also has brown hair but has a patch of white hair. I wonder if he is a chimera. I need to get some test done.

    • Kayla Sheets

      Hi there,
      Feel free to message us if you would like to find out more information about a private consultation. The easiest way is to email us at: or to click the green “contact us” button on the website.

  8. Lena Bodge

    I have A+ blood my husband had O my son has AB+ his sister has A+ same dad.. how is this possible?? Both my son and I have allergies to drugs and metals.. regular MMR boosters and flu shots ,peroxide, bleach,Alfa blockers, beta blockers all antibiotics out side of tetracycline we are allergic to..his sister did not have the same allergies but both her kid’s have them with an auto immune disorder..

    • Kayla Sheets

      Hello Lena,
      Interesting scenario you are describing. I had a client with undiagnosed chimerism who fathered a son with his alternate genome, thus the son had a discrepant blood type from his parents’. If you would like to get more information, feel free to contact us (click the green “contact us” button) or email (

      Best wishes to you and to your family!

  9. Ruth Todd

    The left side of my face has always been different than the ride side… my left eyebrow, eye, and ear are 1/4 inch lower than the right, the left side of my upper lip is fuller than the right. Recently all of my teeth had to be removed due to presistent and chronic periodontal disease and we discovered that the gums on the right side are smooth but the gums on the left have tons of bony bumps and ridges. Also I have a line that starts at the libial frenum and goes all the way to the back of my mouth. I’m able to write with both hands and my hands are different sizes (ring finger on left is 6.5 and on right is 7.5). I’ve always felt that I have a twin that my parents gave away. Is it possible that these are caused from chimerism?

  10. Bryan

    How about mine? I have different skin tone in my forehead and my forehead isn’t flat, the darker skin tone is the lower ground. The lighter skin tone is healthier based on the thickness of my eyebrows. Is that chimerism?

    • Kayla Sheets

      Hi Bryan,
      You also have interesting findings, thank you for sharing this. If you would like to fill out our clinical questionnaire to help us better assess if it is chimerism, please email us at:

      In the subject line simply put, “Chimerism questionnaire”.

      Best wishes to you!

  11. Dorothy Cecchi

    On Chimeriam, this is very interesting. I’m in no way a Chimera. My question is could Chimerism be associated with same-sex attraction. Charles an me have a dear friend who insist that she was suppose to be a man. Ricky has always said that something happened when her Mom was pregnant. Her or her Mom got things mixed up and she has all the looks of a woman but has the brain of a man. In no article can I find this question. If a person has different eye colors, why not the body of one twin and the brain from a deceased twin of the opposite sex. One article had a teenager boy that had internal female organs. Dorothy

    • Kayla Sheets

      Hi Dorothy,
      I think what you are describing is your friend Ricky may have a trans-gendered identity. Your question is very timely, because this is a question I am asked often lately. It makes logical sense that if a person is born with both XX (female) and XY (male) sets of DNA, that it is possible that one is more predominant in their brain cells and the other parts of their body. However this theory needs to be confirmed by studying a large group of trans-gendered folks, and that simply has not happened yet.

      If your friend has any questions, please feel free to have Ricky contact me directly. Our email for general questions is:

  12. Ansar Ali

    My face skin has two different tones. One is fair and other is little bit darker. My left side of the face is little darker and fair skin tones and right side is totally fair. And also on my arms there are white little patches

    • Kayla Sheets

      Thanks for sharing this with us! These skin findings sound very much like a couple of clients we have worked with, and were found to have chimerism. If you are interested in exploring if you have additional findings, you might consider completing our secure online chimerism questionnaire. If so, email us at: It is at no cost, and something we provide for our private clients. Best wishes! Kayla



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