My mum had a history of retained placenta and I asked my OB whether I would have it too. He said it is not heriditary. I had it with DD#1 and luckily I had an epidural as he was pushing and pulling pretty hard to get out what he could, luckily after a while, they managed to get it out but bleeding was very heavy for a few days. With DD#2, placenta came out beautifully and no problems whatsoever! Bleeding was also much, much less.

I hope everything goes well for you with #3.