If it helps any, I conceived (while trying to avoid it) a little over a year post-removal. I had mine removed after a year and a half because of terrible side-effects. My little one is 2 now, and happy and healthy.
Differences between my post-mirena pregnancy, and the 2 prior ones was that I had worse morning sickness (up til delivery), and I had pre-eclampsia after delivery. So keep an eye on your blood pressure during/after your pregnancy when you conceive.