In moderation. It's ok to eat tuna in pregnancy in moderation. It should be fully cooked, not raw. You should only eat one to two servings of seafood a week because seafood has mercury in it. Seafood also has a lot of great nutrients for a developing baby so if you enjoy it, just do it in moderation.
Yes, but . . . Likely that overall benefit of eating tuna well outweighs any potential harm, but tuna may, like shark, swordfish, king mackerel, or tilefish, contain high levels of methylmercury. Mercury can be harmful to your child's neurodevelopment in high concentration. However, fish in general, particularly oily fish, is excellent for neurodevelopment. Get two servings per week.