Actually, caffiene is fine during pregnancy, as long as its in moderation, less then 220 mg a day. The issue with tea is that some herbs and spices can effect the baby, cause miscarriages, ect. There's a long list of what's safe and not, so before you drink any tea just look up the safety of the ingredients.
Drinking tea is fine just limit the consumption. Its the amount of caffeine thats the problem. But one or two mugs of tea a day wont do you any harm. If your concerned just google it and theres many websites that will give you a better breakdown of the different types of tea and the amount of caffeine present.