Iud and periods

I haven’t been able to get In touch with my dr to ask but I was wondering if anyone knows the chances of getting pregnant with the Mirana iud when I still get my regular 4-5 day periods. I got the iud places October 2017 and it’s still in place but I am curious as to if I can’t still get pregnant if I get my periods. I had the skyla iud before never had periods with it and had it removed because the 3 years was up and I got pregnant the first month having it out. Got the skyla put in at my 6week pp check up and it ended up coming out so I went with the mirena. And i am just curious. I’m not trying to get pregnant just trying to get info on the iud because my doctor hasn’t given me much and I have read about a lot of women getting pregnant on this iud