Hi! I have my RNC and I can recommend a few things for taking the test, as well as let you know what it was like.
First off, I had 2 years experience when I took the exam. Although, still green in L&D (only 2 years) the military has accelerated my learning curve ten fold. Nothing like sink or swim.
Okay, I studied 2 books for the exam, and I started studying about a month ahead of time. I used Modules, and AWHONN's Core Curriculum for Maternal-Newborn care. From cover to cover I became intimate with these 2 books up to an hour before the test. Im the kind that likes to cram.
The test I do have to say was very difficult, and like me, the 4 other people that came from my hospital that day to take it we all thought we had failed it. Most of the exam was patho and disease process of your complicated OB cases. Diabetes, HTN, etc.etc. Placental diseases, strips, breastfeeding, PP Hemmorrhage, depression, etc.
Hope that helps, if you decide to certify and you have more questions, let me know.