I just read the entire Prescribing Information for Mirena [Mirena Info] and could find no mention that taking something like Imuran means you cannot have one. People with certain diseases that have increased risk for infection must be evaluated but that does not mean they cannot have one.
Tubal ligation which is a form of sterilization, is not an open abdominal surgery. It is usually done through a very small opening near the belly button [navel]. I guess if you have lots of abnormalities in your intestines, having a tubal might not be possible. I just read that prior abdominal surgery might make a laproscopic tubal impossible. The article said that right after delivery most tubals are done as a mini-lap. You can read all the information here: WebMD: Tubal Ligation
What does your Obstetrician recommend? Hopefully someone here will have more info than I do.