In the Mirena article it states "This device is placed in the uterus where it slowly releases the hormone to prevent pregnancy for 3 to 5 years." I've had my IUD in since February of 2011 so I'm just past the 3 year mark. Since it prevents pregnancy for 3-5 years, how do I know if I'm safe for just the 3 or am good to go for the full 5 years?