First of all, congratulations on deciding to become certified in your field! It is a huge asset to your career development. You will not be sorry. I became certified in Inpatient Obstetrics in 1996 and it has enhanced my career.
Our facility offers preparatory classes for those studying to become certified. I remember I purchased a set of audio tapes and a work book, but I do not remember where I got them. I would try the AWHONN website. I will try and ask our staff develpment department guru and see where she gets the info she presents in class. I also know there are some sample tests available.
Which exam are you taking? There are a couple of different certifications for OB. Since you mentioned L&D I would imagine you will be taking the inpatient obstetrics exam which incorporates labor & delivery, postpartum, and newborn information. It contains fetal monitoring questions and complications of pregnancy questions, and questions about newborn health and some breastfeeding questions.
I'll see what I can come up with for you. In the mean time, obtain an up to date maternity text and read up on things you are unfamiliar with. You will do fine!
Angie