Lydia Fairchild
Lydia Fairchild and her children are the subjects of a documentary called 
The Twin Inside Me .
Lydia Fairchild was pregnant with her third child, when she and the father of her children, Jamie Townsend, separated. When Fairchild applied for welfare support in 2002, she was requested to provide DNA evidence that Townsend was the father of her children. While the results showed Townsend was certainly the father of the children, the DNA tests indicated that she was not their mother.
This resulted in Fairchild being taken to court for fraud for claiming benefit for other people's children or taking part in a surrogacy scam. Hospital records of her prior births were disregarded. Prosecutors called for her two children to be taken into care. As time came for her to give birth to her third child, the judge ordered a witness be present at the birth. This witness was to ensure that blood samples were immediately taken from both the child and Fairchild. Two weeks later, DNA tests indicated that she was not the mother of that child either.
A breakthrough came when a lawyer for the prosecution found an article in the New England Journal of Medicine about a similar case that had happened in Boston, and realised that Fairchild's case might also be caused by chimerism. In 1998, 52-year old Boston teacher Karen Keegan was in need of a kidney transplant. When her three adult sons were tested for suitability as donors, it was discovered that two of them did not match her DNA to the extent that her biological children should. Later testing showed that Keegan was a chimera, a combination of two separate sets of cell lines with two separate sets of chromosomes, when a second set of DNA was found in other tissues. This DNA presumably came from a different embryo than the one that gave rise to the rest of her tissues.
Fairchild's prosecutors suggested this possibility to her lawyers, who arranged further testing. As in Keegan's case, DNA samples from extended members of the family were taken. The DNA for Fairchild's children matched that of her mother to the extent expected of a grandmother. They also found that while the DNA in Fairchild's skin and hair did not match her children, the DNA from a cervical smear test was different and did match. Fairchild was carrying two different sets of DNA, the defining characteristic of a chimera.

# Sources
- ABC News: She's Her Own Twin Article on Lydia
- Kids' DNA Tested, Parent Informed The DNA Is Not A Match Article on Lydia's case
- The Stranger Within Article on Karen Keegan's case
- Genetic Mosaics Discussion on Teragametic Humans
- DNA Tests Shed Light on 'Hybrid Humans' NPR recording.
- Mayne, Eleanor (March 5, 2006). "The mother with three children who don't share her DNA - and why her astonishing story will throw doubt on the 'foolproof' evidence in thousands of court cases". The Mail on Sunday, London. pp. 1819..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"\"""\"""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{display:none;font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}