Never been pregnant, but there are some things you need to eat to ensure that your baby is healthy:
B12 (an active source, not from seaweed or algae)
iron (pregnant woman can get anemic easily)
Omega 3 fatty acid
Of course, you need all of the vitamins and minerals, a lot more then normal, but your calorie intact doesn't increase much. You need to be mindful of eating lots of healthy food and a wide-range of it.
Becoming Vegan has a great vegan pregnancy section, which should get you started. You may also want to talk to a dietitian if you don't know your requirements. Also, a pregnancy multi-vitamin would be a good idea if you aren't confident in your eating habits.