Highly unlikely. Due to the hormones in the Mirena it causes what many women would call pregnancy symptoms. I believe you need to take a pregnancy test prior to getting the mirena in anyways (I know I did when I got my IUD in) and the odds of pregnancy on the IUD are less than 1%. Beyond sterilization and the shot they're one of the most effective birth controls.
This is probably just the hormones causing this! If your pregnant, than it would more than likely be a pregnancy in the tubes & it would to have just happen, before they do an iud they do a pregnancy test just to make sure! so I highly doubt it!