Often the philosophy is stay on the medications that got you unti remission, in order to sustain remission, why risk tapering. I understand on pregnancy risk and 6mp. It's a personal choice. Biologics are safer for pregnancy (remicade, humira, etc.).
Here's a couple links on ibd medications and pregnancy, I think 6mp is a class D medication:
From conception to delivery: Managing the pregnant inflammatory bowel disease patient
www.wjgnet.com/1007-9327/pdf/v20/i13/3495.pdfThe Second European Evidenced-Based Consensus on Reproduction and Pregnancy in Inflammatory Bowel Disease
ecco-jcc.oxfordjournals.org/content/eccojc/9/2/107.full.pdf