If you have a wide variety of acute care experience, you'll be just fine. I am guessing if you've only done OB/GYN and this is an OB/GYN pathology specialty, you'll also be fine.
I transitioned fairly easily into pathology after several years of acute care experience. I did have trouble with immunostains and abbreviations that are different from anything I had done, but there are web sites where you can get yourself a print-out, or ask them to share what they can with you.