Storing Breastmilk


I know everyone is different in terms of supply but how much breastmilk do you think is reasonable to save up during 12 weeks of maternity leave? I work with chemistry at work that could be harmful to my supply so I am afraid I womt be able to pump or nurse once I return to work. I am hoping to save up as much as possible before returning so we can go a little while before fully transitioning to formula. I feel bad for not being able to nurse longer but in my career field it really isn't an option unless I stay out of our lab like I am during the pregnancy. I just don't know how that would go over with my employer.