Maternity Leave / Work Putting Pressure on Me

Ugh, I am so frustrated with my job.  They hired a girl to cover my year long mat leave but she did not work out.  She was lazy and didn't listen to instruction and called in sick at least 1 day each week of the 3 she was working.  So, yesterday they fired her.
Anyway, now they are looking for her replacement and I have expressed my concern about being able to train someone else in the time provided.  I'm due Aug 6th and would like to work until Aug 4th.  I say that I would LIKE to.  My boss is just expecting me to be able to like it's nothing.  He's all like "oh you'll go late" and "you better not go into labour early because we need you here."  Like, how the hell can I promise that???  I can't promise my baby won't come early.  I cant promise that I won't be too damn tired to work!  This is stressing me out and causing me anxiety at a time that I really don't need it.  10 years at this company and they expect me to go like a fracking work horse until the very end.  The pathetic thing is that they claim they are so family friendly and accommodating but really it's the exact opposite.