According to EWG, pregnant women should avoid the following types of fish:
Gulf Coast Oysters
Recommended no more than one serving per month:
Great Lakes salmon
Gulf Coast blue crab
Channel catfish (wild)
Lowest in mercury:
Blue crab (mid-Atlantic)
Salmon (wild Pacific)
* Shrimp fishing and farming practices have raised serious environmental concerns.
** Farmed catfish have low mercury levels but may contain PCBs in amounts of concern for pregnant women.