When to leave work

Me
I plan on taking my 12 weeks as allowed by Family and medical leave act. I work retail/service and have to stand alot and minor lifting. I'm 23 weeks now and fair well at work most days. I'm wondering how many weeks prior to my due date is should take leave. I thought 2 weeks but my sister had her first child at 37 weeks. I definitely don't want to be at work when it happens. I don't even think I will be returning after the 12 weeks are up, my husband wants me to stay home with the baby.(I want to too) I plan on breastfeeding and the small company I work for has no proper place for breast pumping. I don't want to file any legal action against them. I can't make them build a room for me when it's physically impossible. Should I take leave early?