when i was an undergrad i was under the impression you had to tell them, well atleast where i was, you had to get certificates to say you were right to work and what you could and couldnt do (seems a bit over the top to me now) but i only found that out from a nother girl, and she was in her 2nd tri by the time placements were on. and i think it was more the lifting etc...anyway...i would tell them, just make it easier and you can then have their support with what you can and cant do rather than you just saying 'i cant look after that pt' but not tell them why cause that would be bad...