I don't know how it is where you work, but some places can't discriminate for health reasons. I went to an interview pregnant before and they had to interview me and didn't bring up the pregnancy directly (I was about 6 or 7 months along so it was obvious). Turns out they didn't care about the pregnancy, they really needed help and were willing to train me before the baby came.
To be safe, if you want the job, maybe you should interview at the end of the week and then let them know about the surgery when it is scheduled? Do you think they would fire you or move you back to your current job?