The mirena is a great contraceptive. Yet it is not for all women. Like all other contraceptives, ( birth control medications ), it is not guarenteed to prevent a pregnancy. Though the odds are quite slim, they are still there. The mirena secretes a steady flow of levonorgestrellevonorgestrel into the uterus for up to five years. The possibility of getting pregnant the same day of removal all depends on your body and how long the mirena was in place. More than likely if a pregnancy does occur it will be an ectopic pregnancy which is a pregnancy that happens in the fallopian tubes.
If you are having sex you should always use protection, such as a condom. Not only for the prevention of a pregnancy but also for the prevention of an STD. Unless you and your partner are 100% sure you both are STD free a means of protection is always the safest bet.
AOL Health