Vegetarian while pregnant

So I was talking to my dude about getting pregnant in the future (neither if us are ready yet) and I just started transitioning to a mostly vegetarian/pescatarian diet. I've cut out red meat and chicken and am subbing tuna/salmon and other lean fish for it and will be eating complex carbs like brown rice, quinoa and other grains and legumes for extra protein. Obviously I love veggies so I mostly snack on those or sometimes low carb/gluten free crackers. I'm also keeping eggs, some dairy (homemade yogurt, light goat cheese) and honey.

My boyfriend was asking if I would transition back to eating meat in the event that I become pregnant, he feels that me being veggie while pregnant could harm me or baby or we both might not get our proper nutrients. Again, this is all hypothetical since I'm not actually pregnant but just curious.

Come to think of it, I've never asked or thought about what a pregnant lady should do if she's also vegetarian or vegan. Can this lifestyle still be maintained?