Fish is an excellent source of protein, minerals, and healthful fatty acids, making it an important component of the pregnancy diet. However, some fish contain high levels of a form of mercury known as methylmercury. If a pregnant woman consumes too much methylmercury on a regular basis, it may harm her unborn child's developing nervous system. Therefore, there are certain types of fish that pregnant women, in addition to women who may become pregnant or are breastfeeding, should avoid or limit.

Why the Concern?

Mercury is an element that occurs naturally in the environment and also can be released into the air through industrial pollution. The mercury then falls from the air and is absorbed into the surface water, eventually ending up in streams and oceans. Bacteria that live in the water cause mercury to change into the toxic form, methylmercury, which is a toxic form. As fish feed on plants and organisms in the water, they absorb methylmercury. This methylmercury can damage the nervous system of a developing child.

Most fish contain some methylmercury, but large fish that feed on other fish and live long lives accumulate the highest levels of methylmercury in their bodies. These are the fish most likely to cause adverse effects because of their high methylmercury concentration. The United States Food and Drug Administration (FDA) recommends that pregnant women, women who may become pregnant, nursing mothers, and young children avoid fish with high levels of mercury and limit others.

Fish to Avoid

• Shark
• Swordfish
• King mackerel
• Tilefish

Fish to Limit to 6 Ounces Per Week

• Tuna (except canned light tuna, which can safely be consumed in amounts up to 12 ounces per week)

What About Other Types of Fish?

There are certain types of fish that have lower-than-normal levels of mercury. Some commonly eaten fish and shellfish that are low in mercury include salmon, shrimp, canned light tuna, pollock, and catfish. Mercury levels may vary depending on where the fish was caught; check with your local health department regarding the mercury levels of fish caught in your area.

A safe amount to eat is 12 ounces (about two average meals) of cooked fish per week. A serving of fish is typically 3-6 ounces, but be aware that portion sizes in restaurants tend to be larger.