Since you know when baby is coming, it might be easier to fill the bags at home, but you won't need to fill the bags while the baby is so young .... perhaps half full. If you can, I would try to just use the milk you are producing for the first week.
How many times a day are you pumping and how long were you on the protocol? Also, do the suction cup attachments fit you properly?
If you do need to use formula at the hospital, I would suggest you use the ready to feed that the hospital has ... it will flow easier through the lactaid and you will not have to try to use the formula strainer .. that little thing is easy to lose and you would need to bring vinegar to properly clean it so it does not get clogged. Also, the hospital should give you a small supply of the ready to feed bottles to take home .. they usually carry both Similac and Enfamil .. I recommend the Enfamil.
Make sure you bring some paper tape with you and practice taping and positioning the straw with you.
Your sister's collostrum may not come in until the third day, so hopefully she won't mind pumping for you until it does come it.
Keep up the good work!
