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, but it can also 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. As fish feed on plants and organisms in the water, they absorb methylmercury.

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. Because of their high methylmercury concentration, these are the fish most likely to cause adverse effects. The United States Food and Drug Administration (FDA) and the Natural Resources Defense Council (NRDC) recommend 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
• Big eye or ahi tuna
• Marlin
• Orange roughy

Fish to Limit to 6 Ounces Per Week

• Albacore (white) tuna

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 2-3 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.

Updated fish consumption advisories for where you live are available from the United States http://www2.epa.gov/fish-tech (EPA) website. If you want to keep tabs on how much mercury you are consuming when you eat any kind of seafood, you can find details on the https://www.nrdc.org/stories/smart-seafood-buying-guide website.