Obstetrics?

Maybe I will change my mind when I'm done school, but for the moment working as a nurse in obstetrics would be my ultimate dream. I am obsessed with birth and everything that it entails....so my question is....how big is the demand for obstetrical nurses and do you have to try all other departments first?? I would love to do a placement in obstetrics when the time comes. Also, after four years of Bachelor of Science in Nursing studies....could one start off in obstetrics right away??

Thanx in advance!
~*Lucie