Hi Iris,
Have a lot of info here....and differences for various types of practice. Please know that I do not practice OB...I'm critical care...however some of the answers are universal for nurses in general...
Speciality is not necessarily required. An RN license will qualify a nurse to practice in a general OB unit, clinic or physicians office. I know that an advanced degree is avaliable but I'm not even sure about a certification.
Continuing ed requiremenats vary....unless your facility has certain requirements, or you have a speciality...the only requirements would be what ever is required to renew your license...and that varies state to state.
Hope this helps...Bonnie