Theoretically, a woman can get pregnant as soon as her IUD is removed. However, anecdotal evidence suggests that the time it takes a woman to conceive (post-IUD) varies greatly.
This depends on the individual but as soon as mirena is removed the body starts to create the hormones necessary to have normal monthly ovulation again, you can get pregnant.
According to experts, you may get pregnant soon if you have sex after removing mirena. This is because of the fact that contraceptives does not work if mirena is removed.