Fish and seafood can be a valuable source of nutrition. Fish contains protein, omega-3 fatty acids, vitamin D, and other essential nutrients that make it an exceptionally healthy food for pregnant mothers and developing babies. However, some fish can contain harmful levels of methylmercury, a toxic mercury compound. Mercury occurs naturally in the environment and is often released into the air through industrial pollution. From the air, mercury can fall and accumulate in steams, lakes, and oceans where fish is caught for consumption. Bacteria in the water can cause chemical changes that transform mercury into the toxic form of methylmercury. Fish in these bodies of water absorb methylmercury as they feed on organisms within the water.

Harmful Effects

If consumed regularly by women who can become pregnant, women who are pregnant or nursing, or by a young child, methylmercury can harm a developing brain and nervous system. Just about all types of fish contain trace amounts of methylmercury, which is not harmful to most humans. However, larger fish that feed on other fish accumulate the highest levels of methylmercury. These types of fish pose the greatest risks to people that consume them on a regular basis. Pregnant women as well as women who are trying to conceive, nursing mothers, and young children are advised to also avoid these types of fish in large amounts. Women can avoid any risks associated with methylmercury and still get some of the important health benefits of fish by following the guidelines described in the following section.

Fish Guidelines

Any risk comes from a buildup of mercury in the body and not from a single meal. The Food and Drug Administration (FDA) and Environmental Protection Agency (EPA) have released specific advice concerning fish bought from stores and restaurants, which includes ocean and coastal fish as well as other types of commercial fish. If you follow the advice presented by the FDA and EPA, you can gain the positive benefits of eating fish while still avoiding any developmental problems to your baby due to the mercury content of fish. The FDA and EPA advise women who are pregnant or could become pregnant, nursing mothers, and young children not eat shark, swordfish, king mackerel, or tilefish because these fish contain higher unsafe levels of methylmercury.

Levels of methylmercury in other fish can vary. As a result, these agencies also advise that women who can become pregnant, women who are pregnant, and nursing mothers eat up to 12 ounces (2 average meals) a week of cooked fish or shellfish that are lower in mercury. Five of the most common fish that are low in mercury include shrimp, canned light tuna, salmon, pollock, and catfish. They also advise eating a variety of fish and shellfish and not eating the same type of fish or shellfish more than once per week.

If the fish is caught by family and friends in local lakes, rivers, and coastal areas, you should check local advisories about the safety of the type of fish caught. If no information or advice is available, you are advised to eat up to 6 ounces (one average meal) per week of the fish that was caught in local waters but don't eat any other fish during that same week. Follow these same guidelines for young children but with smaller portions. These guidelines are important when it comes to keeping the total level of methylmercury, contributed by all fish, to low levels in the body. It is smart to keep abreast of guidelines concerning the consumption of fish during pregnancy. Many organizations are trying to enforce stricter guidelines than are currently being recommended by the FDA and EPA. Check out the EPA Web site, at www.fda.gov for the latest advisories.