Hey mama, tahong is generally safe to eat during pregnancy as long it's cooked thoroughly, raw or undercooked shellfish can carry harmful bacteria na hindi gusto natin, so make sure well-cooked talaga! Since you're already at 31 weeks, best to check with your OB din just to be sure based on your specific health situation, pero most moms I know naman ay kumakain ng tahong without issues as long they're properly prepared.