I totally understand your situation! I was starting my last semester of nursing school when we planned our first baby. I was about 18 weeks along by graduation. It worked out great because I was blessed to have no sickness or anything to affect my schooling.
I got my first interview for one position when I was about 8 mos pregnant (shortly after i passed NCLEX) and was actually told that was why I wasn't offered the job...which is discrimination, and not legal. It was hard getting an interview to begin with, being a new RN.
Regardless, my advice is to start trying if its what you both really want, but as you mentioned in your post, keep in mind, all pregnancies are different. There's always a chance your last several months of school could be extra grueling if you're sick. And even though its not right, my opinion is that being pregnant could affect your chances of hire.
I ended up getting a job eventually anyway. It's good to weigh out your desires and priorities at this point. Having a little sibling for your little one would just possibly delay starting your nursing career... Or not! Maybe just think if that is a risk you are willing to take. I know that I had absolutely no regrets about the timing of my pregnancy whatsoever!
Good luck to you!!!