Many women who get pregnant wonder if they can safely continue their vegetarian or vegan pregnancy. The answer is you absolutely can! The first thing you should do is let your Ob/Gyn know. If you have one that frowns when you say it, find a new one! Your doctor needs to be supportive of your lifestyle choices.
There is a pretty good book on the topic, called "Your Vegetarian Pregnancy" by Holly Roberts. You can probably pick up up a copy pretty cheap, especially if you search around the auction sites. If you go with the other non-vegetarian books, just ignore the sections where they tell you how many animals you need to eat during that nine month period.
Within the last five years I have had two vegetarian pregnancies and I have written a couple of articles on the topic. They include information you need to know about nutrition, as well as tips from others who have had a vegetarian or vegan pregnancy. You can find them here:
Another good thing to do is join the Vegetarian Resource Group's discussion group, where you can chat with others who have had vegetarian pregnancies.
In addition, you can find some good information about vegetarian and vegan pregnancy by visiting the Physicians Committee for Responsible Medicine site. They have information on Vegetarian Diets for Pregnancy, as well as the Vegetarian Advantages for Children, vegetarian diets are right from the start, and have a list of healthy snacks for vegetarian kids.