The families, who live in the Ural Mountains in western Russia, only found out when one of the fathers refused to pay child support for his daughter Irina following a divorce earlier this year, saying she did not look like him.
His ex-wife Yuliya Belyaeva took him to court, but DNA tests revealed that neither of them were Irina’s parents.
“The judge couldn’t believe it,” Ms Belyaeva said. “She said she’d only seen cases like this on TV and didn’t know what to advise us.”
Ms Belyaeva said she thought back to the day she gave birth to her daughter in December 1998 and realised there was another woman in the ward with her at the same time.
“I made a photocopy of the DNA test results and went straight to the prosecutor’s office,” Ms Belyaeva said. “There I lodged an official complaint about being given the wrong baby in the maternity hospital.”
Prosecutors searched for Belyaeva’s daughter – and found her at the other end of town.
“As soon as I saw her, it was like looking at a copy of me as a child,” Ms Belyaeva said.
“At that moment I didn’t need any DNA test result to tell me this was my daughter. … Anya, was blond and looked just like me and my ex-husband. And our daughter was dark-skinned and had dark hair and looked like the other father. He’s a Tajik, and she looked just like him.
“Suddenly my whole world turned upside down and inside out. I always thought that Irina looked a little bit like my mother-in-law. She had dark hair, too, and dark eyes. It never occurred to me that Irina wasn’t my real daughter. I never believed doctors could make that mistake.”
But both daughters refused to return to their birth parents, saying they preferred to stay with people who had raised them.
“Irina keeps saying to me: ‘Mum, please don’t give me away!”‘ Ms Belyaeva said.
“I comfort her by saying: ‘I would never do anything against your wishes. Nothing has changed. I’m still your mother.”‘
Ms Belyaeva said she said hasn’t met Anya often and that she was being brought up in a very different family environment.
“The other family are Muslim. So my biological daughter was brought up as a Muslim. They have completely different traditions and customs. That makes it even harder.”