The U.S. Food and Drug Administration suggests that pregnant women limit their total intake of fish and shellfish, including crab legs, to 12 ounces or less a week. Twelve ounces equates to two-to-three meals containing shellfish.
The FDA provides limits on shellfish and fish consumption for pregnant women due to the risk of mercury exposure. At high concentrations, mercury causes irreversible damage to a fetus' nervous system. Nearly all types of fish and shellfish have some level of mercury in their bodies, but shellfish pose little threat when consumed within the advised amounts. The recommendation of 12 ounces of total fish and shellfish a week serves as a rough guideline. This amount should be lowered if a pregnant women also eats foods like albacore, which contains moderate levels of mercury. If a woman consumes 15 ounces of shellfish one week, she can remain within the safe zone by avoiding it the next week.
According to the FDA, pregnant women also need to ensure that the shellfish they eat is thoroughly cooked. Foodborne bacteria, such as salmonella and listeria, pose a serious risk to the mother and child. Mayo Clinic states that shellfish, including crab, is considered fully cooked when it has a milky-white appearance. The internal temperature needs to measure at least 145 degrees Fahrenheit.