I would ask your teacher if you could make it up after you had your baby and explain why. Good Luck
The studies that I have read seem to indicate that it is safe in later pregnancy. Although it appears inconclusive during any stage of pregnancy. I would contact your dr to see what he has to say about it or see if you could take the class next semester. I am sure, however, that a lady in my A&P class dissected during pregnancy. I don't remember exactly how far along she was, however. Also, talk to your professor and he may know. I would guess that the room is very well ventilated, plus you'll be wearing gloves. Good luck with the nursing program, you won't regret it.
Literature has shown that Formaldehyde exposure can cause early termination (miscarriage), as well as a multiude of birth defects both developmentally and physically. I am not sure how much exposure one needs for these potential risks to occur but I know if I were in you shoes, I would absolutely refuse to be exposed to formaldehyde. Hope this helps.