Warming partially thawed BM?

We've started using some of our freezer supply of frozen breast milk: we follow the protocol of placing in fridge to thaw, but the thawing takes longer than 12 hours. I can't find info online anywhere if you need to wait for the milk to be fully fully thawed before transferring to bottle and warming, or if you can transfer to a bottle while it still has some frozen bits left in it and warm that way?