Interesting that they said not to use arnica while pregnant. I was advised to take arnica in the weeks leading up to my due date to help with healing afterwards. My friend's MW in NZ also recommended she take it before she gave birth and she had no probs.
As it turned out, I didn't take it before I had C as he was unexpectedly very early. Maybe it's "OK" to take close to your due date because you're so close anyway?
Be interesting to hear what your MW says about it if you ask
Hope you work out why you're bruising more easily

My (unprofessional!) guess would be something to do with increased blood flow during pregnancy?