Crab legs are low in mercury, so they are safe for pregnant women to eat in moderation. It is important for pregnant women to make sure the crab legs are cooked thoroughly prior to eating them.
According to the American Pregnancy Association, pregnant women can safely consume up to 6 ounces of crab legs twice per week. Limiting consumption to this amount helps to ensure that any mercury in the crab legs doesn't affect the baby's nervous system; large amounts of mercury can cause nervous system damage in humans.
Any seafood eaten by a pregnant woman, including crab legs, must be fully cooked. Seafood is thoroughly cooked when it reaches an internal temperature of at least 145 degrees Fahrenheit.