Don't plan on delivering during the last semester. That would be no Bueno as you will have clinical hours to complete, with likely little flexibility.
Also, if you wait until you have a job offer, you won't be covered by fmla until you've been there a year... and maybe not even short term disability for a while (6 months I see quite a bit).
If you can plan it perfectly, I would get pregnant over a summer break, if you can financially swing that before graduation. Or immediately after graduation. Or after your first year of nursing.
However, those are big ifs. It takes couples an average of 6 months to get pregnant. It took me and my husband 15 months with our first and 8 months with our second... that's with doing all the things and not having anything wrong. So surprise! It may not be that easy to pick when you get pregnant or give birth. Ultimately, it'll happen when it happens.... and you have to be flexible to an extent.