Can a tooth that had a mercury filling be harmful to unborn baby if tooth has chipped and i swallowed the bit of tooth i am 26 weeks pregnant

Absolutely not!: There is nothing to be concerned about. Only elemental mercury could be harmful. Once combined as part of a hardened amalgam filling, there is no danger. Congratulations and good luck.

Nope: Your baby will not be harmed by any broken teeth or fillings. Have the tooth looked at by your dentist. There's a reason it broke, and it may need to be treated before you give birth.