Lydia Fairchild (born 1976) is an American woman who exhibits chimerism, having two distinct populations of DNA among the cells of her body. She was pregnant with her third child when she and the father of her children, Jamie Townsend, separated. When Fairchild applied for enforcement of child support in 2002, providing DNA evidence of Townsend's paternity was a routine requirement. While the results showed Townsend to certainly be their father, they seemed to rule out her being their mother.
https://en.wikipedia.org/wiki/Lydia_Fairchild