H.C.
My sil got pregnant w/an IUD...she'd had it in for over a year, maybe 2 yrs. Without her realizing it, it has slipped out of position, allowing her to become pregnant. She found out when she had an early miscarriage. Having said that...depending on what type of IUD you have in, you may stop getting periods altogether. I think the Mirena IUD is supposed to gradually completely elimate periods.