I'm currently pregnant (32 weeks), and I work in pediatric intensive care. It's been very difficult to find appropriate patient assignments without effecting the workings of my unit.
I spoke to my OB first and foremost about what patients are appropriate for me. In the very beginning, I had no weight limit, so that wasn't an issue. However, H1N1 was a big concern, as we had an abundance of it in my unit, and as the CDC was reporting it to be very dangerous to pregnant women. My OB wrote me a medical excuse, saying "NO H1N1 patients."
As far as CMV, my ob tested me for it - I thought for sure I'd have antibodies already and have nothing to worry about, but surprisingly, I don't. So I am excused from taking CMV patients as well. CMV is one of the TORCH diseases, so it's really not worth the risk to care for them when you have no immunity.
The only other things I avoid are patients receiving chemo and patients who need to be taken to radiology procedures (CTs, extensive x-rays, etc.) Also, since my uterus is now out of my pelvis, I am not to solely lift more than 30 pounds, so they try to assign me lighter patients.
The end result is that I have to be very flexible about everything else - I have to take up the slack some how, and that usually occurs by me taking more admits, taking more of the chronic patients, etc - those things that aren't the most fabulous assignments, but are safe and free up everyone else to do what I can't.