There are certainly examples of this, a well-known one is the story of Lydia Fairchild. The mother of two, and her husband were expecting their third child when they decided to divorce. DNA samples are taken from the father and mother who want to receive state funding for their children. While the father's DNA matched the children's, the mother was found to be genetically unrelated to the children. Fairchild, who gave birth to the third child under surveillance, was tested for DNA as soon as the child was born, and it did not match the third child. This is known in biology as 'chimerism'.
A woman (Here the woman we talk about is Fairchild's mother) gets pregnant by two different men, and due to some complications, one of the children cannot develop on its own. Instead, it grows up in a kind of synthesized form with the other baby that the mother carries and continues to exist inside the child that is born. To give an example, the child is born with 'its own hair but not its own eye'. The mother of all three children born to Lydia Fairchild is actually her twin, who clung to her while she was still in her mother's womb and made a place for herself in this world.
