is it possible to get pregnant with an iud?

I have the skyla iud and I get my period on it like clock work, I start on the 20th every month and it only last for 5 days and im a day late so I'm not worrying yet because I know there are a lot of factors that could cause a period to be late. So just wondering if I could get pregnant with an iud. My last ob told me I couldn't get pregnant got my iud taken out because it was at the 3 year mark and when it would have been time to get my period I missed it and took a test and it was positive so I have a lot of things happen to me that are almost impossible.