I told my agency when I fell pregnant with Lachlan because I was in factory work and didn't want to be put into a position that consisted of heavy lifting, and they said most of the preg girls they have had worked till 7mths. I quit working at 5mths

Not sure what sort of work you are doing, but if it wont endanger your baby, you don't want to tell them you don't have too till you are ready.

Love