Labor and delivery is a hard specialty to get into. Many people want to work there and many nurses work there for a long time. Jobs are scarce and most, if not all, will want experience.
My advice would be to do really well in nursing school
, particularly in your OB clinical. Make friends with the clinical instructor and faculty instructor because you will probably need their recommendation and connections in the future. Working in OB or LD as a secretary, nursing tech, or even as a receptionist at an OB practice would be a good way to get your foot in the door. Also, do some shadowing on the LD unit while you are in school and make friends with the nurses and managers. Do your partnership or capstone in LD if possible or in OB at least. Apply for summer externships in LD as well. When it comes time to apply for jobs, make sure you have an excellent resume that highlights your LD experience and great recommendations from LD faculty and staff.
Keep an open mind. There are many, many areas of nursing and until you have experienced them it's hard to decide which you like and don't like. You might go into nursing school and find that you fall in love with a different specialty. I thought I wanted to do OB when I started nursing school, but once I had the clinical I decided there was not enough variety or technical skills for me and I ended up accepting a position in a Pediatric ICU. It doesn't get more technical than that!
I hope this was helpful to you. Good luck!