what is a nurse practitioner specialty called in an ob office?

Hi Im new to the site and I was wondering what is the specialty of a np that works under a obgyn? Im starting school for nursing and im working on my adn and a school locally offers a rn-msn that I want to go for after i graduate.Then I noticed that they only offer 4 specialties and I really want my specialty in ob. I know they offer a family nurse practitioner program but not sure if thats what I need.I live in huntsville,al so if anyone lives here and could give me some tips that would be great. Any insight will help.

p.s
I have called the school but had to leave a msg waiting on a call back.

Thanks
I believe you are looking to be a Women's Health NP or a Certified Nurse Midwife.