Just because you are pregnant doesn't mean you have to diverge from your vegetarian diet. Your baby can receive all the nutrition he or she needs to grow and develop while you follow a vegetarian diet, if you make sure you eat a wide variety of healthy foods that provide enough protein and calories for you and your baby.
Depending on the type of vegetarian meal plan you follow, you may need to adjust your eating habits to ensure that you and your baby are receiving adequate nutrition. You should consume about 300 more calories than you did before you became pregnant. Discuss your diet with your doctor.