(MayoClinic.com) If you're pregnant, you may feel like you need to become a nutrition expert overnight. After all, what you eat and drink — and what you avoid — influences your baby's development. Some choices are logical, such as eating plenty of fruits and vegetables and eliminating alcohol from your diet. But what about seafood? When it comes to pregnancy and fish, researchers give mixed reports.

Here, Roger Harms, M.D., a pregnancy specialist at Mayo Clinic, Rochester, Minn., and medical editor-in-chief of MayoClinic.com, offers practical advice about pregnancy and fish.

Seafood can be a great source of protein and iron — crucial nutrients for your baby's growth and development. And the omega-3 fatty acids in many fish can promote your baby's brain development. Research has shown that skimping on seafood during pregnancy may contribute to a child having poor verbal skills, behavioral problems and other early developmental issues.

But some types of seafood — particularly large, predatory fish such as shark, swordfish, king mackerel and tilefish — may contain high levels of mercury. Although the mercury in seafood isn't a concern for most adults, special precautions apply if you're pregnant or planning to become pregnant. If you regularly eat fish high in mercury, the substance can accumulate in your bloodstream over time. In turn, too much mercury in your bloodstream may damage your baby's developing brain and nervous system.

Some types of seafood contain little mercury. The Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) say pregnant women can safely eat up to 12 ounces a week (340 grams) or two average meals of:

• Shrimp
• Canned light tuna (limit albacore tuna and tuna steak to no more than 6 ounces a week)
• Salmon
• Pollock
• Catfish

But some research suggests that limiting seafood during pregnancy may do more harm than good, since the risks from losing important nutrients may exceed the risks of harm due to mercury exposure. A 2007 British study found that women who ate 12 ounces (340 grams) or less of seafood a week were more likely to have children with verbal or other communication problems at age 3, and behavioral problems and trouble with fine motor skills by ages 7 and 8. No negative effects were noted for women who ate more seafood than the FDA-approved guidelines.

Consider these precautions:

• Avoid large, predatory fish. To reduce your exposure to mercury, don't eat shark, swordfish, king mackerel or tilefish.
• Avoid raw fish and shellfish. To avoid ingesting harmful bacteria or viruses, avoid raw fish and shellfish — especially oysters and clams — and anything you know was caught in polluted water. Refrigerated smoked seafood, such as lox, also is off-limits.
• Understand local fish advisories. If you eat fish from local waters, pay attention to local fish advisories. Larger game fish contaminated with chemical pollutants may potentially harm a developing baby. If advice isn't available, limit consumption of fish from local waters to 6 ounces a week and don't eat other fish that week.
• Cook seafood properly. Cook fish to an internal temperature of 145 F (67 C). The fish is done when it separates into flakes and appears opaque throughout. Cook shrimp, lobster and scallops until they're milky white. Cook clams, mussels and oysters until their shells open. Discard any that don't open.

While research has shown that women who take fish oil supplements during pregnancy may improve their children's hand-eye coordination, the findings are preliminary. It's important to keep in mind that fish oil supplements aren't uniformly tested for the presence of mercury. The safety of fish oil supplements during pregnancy also has yet to be established, and more studies are needed before they can be routinely recommended during pregnancy.

Though mercury can harm a developing baby's brain, eating average amounts of seafood containing low levels of mercury during pregnancy hasn't been shown to cause problems. And the omega-3 fatty acids in many types of fish — especially salmon and tuna — promote healthy fetal development. As long as you avoid fish known to be high in mercury or contaminated with pollutants, fish can be a regular part of your healthy-eating plan.

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