Time to do lots of research! You will want to explore how you want to birth- at home, birth center, or hospital. You can go to the "Finding Your Tribe" forum on MDC to see if you can find any recs for OBs/midwives. Don't be afraid to interview several or to switch care if you find that you are not seeing eye to eye with the person that you choose. Ask about c-section rates for your dr and for the hospital. There are some places with c-section rates or 50% or more, and this you want to avoid, avoid, avoid!
Have a list of questions when you go to meet with potential caregivers, and make sure they give you the answers you want/need. Also, don't feel like there is a huge rush to choose someone. You are only 4 weeks along, and prenatal care at this point is going to be advice about nutrition, vitamins, and exercise, and you can find all of this info yourself online or in books.
A great book to read is The Thinking Woman's Guide to a Better Birth but Henci Goer. Lots of info there, including advice on how to choose a caregiver.
mama to Ingrid (11/06) and Louisa (5/29/09):