Get a bottle warmer. Test it before you give it the baby. And if you do use the microwave warm water in a mug and then set the bottle in it. I had to use FORMULA with my first and my mom taught me all about it.
Go to Medela's website and they tell you how to store and thaw milk.
OMG I just give it to her room temperature, like I have a gallon of water I buy at stores and wash the bottle and put the water in there followed by formula then give to her. Should I be warming it up first?? She drinks it all fine.
You warm the bottles in water
It cooks unevenly in the micro And the plastic from the bag melts into it. You have to slowly warm it on the stove top in a pot of water making sure the bag doesn't touch the sides or bottom or the bag will melt.