I had my first Mirena in for 2 years, had it removed in April 2010. I had my daughter April 2011. We waited 3 months before trying and got pregnant on our first try.
I just had my second Mirena removed on Dec. 17th, 2012. This is our first months trying, so we will see what happens. My OBGYN told me that it leaves your system instantly and she told us that we can start trying right away.