A good rule is to think of herbs in three categories, nourishing, tonics and medicinal (see herbalist Susun Weed's books. She has one for the childbearing year that is a great reference.). The nourishing herbs are fantastic for pregnancy, especially nettles and oatstraw. Nettles builds the blood and prevents swelling and is packed with vitamins and minerals. Oatstraw is really calming for the nerves and has lots of calcium other nutrients...all the benefits of oatmeal, really. Red Raspberry is a tonic herb, and is best in the second or third trimester.
Trust your body to know which herbs to avoid. If they are bitter or overly strong tasting (medicinal), you want to steer clear, but your body will know that if you listen. I bet you could do a google for a good list of herbs to avoid, but for the most part they are not things you would commonly come across. Of course, massive amounts of parsley, oregano, ginger, etc. aren't great, but you would have to take a LOT all at once. Regular amounts in your diet is fine.
Good luck!