Pregnant women generally have weaker immune system. Also, raw food may contain bacteria that cause food poisoning such as Salmonella, E. coli and Listeria. In particular, Listeria may cause miscarriage, stillbirth or preterm delivery.
Cooked sushi is fine, except tuna/swordfish, which are high in mercury. Any raw food may potentially be harmful to mummy, and sometimes cause developmental problems with baby