Karen Schroeder Kassel, MS, RD, MEd
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.
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. 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.
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,
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.
Updated fish consumption advisories for where you live are available from the United States
Environmental Protection Agency
(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 a mercury thermometer on the
Center for Food Safety and Applied Nutrition
Environmental Protection Agency
Dietitians of Canada
Health Canada Food and Nutrition
Davidson PW, Myers GJ, Weiss B. Mercury exposure and child development outcomes.
Pediatrics. 2004; 113(4):1023-1029.
Fish consumption advisories. United States Environmental Protection Agency website. Available at: http://water.epa.gov/scitech/swguidance/fishshellfish/fishadvisories/index.cfm. Accessed January 9, 2014.
Mercury contamination in fish. Natural Rescources Defense Council website. Available at: http://www.nrdc.org/health/effects/mercury/protect.asp. Accessed January 9, 2014.
Mercury levels in fish. American Pregnancy Association website. Available at: http://americanpregnancy.org/pregnancyhealth/fishmercury.htm. Updated January 2013. Accessed January 9, 2014.
Nutrition in pregnancy. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated October 28, 2013. Accessed January 9, 2014.
What you need to know about mercury in fish and shellfish. United States Food and Drug Administration website. Available at:
http://www.fda.gov/Food/FoodborneIllnessContaminants/BuyStoreServeSafeFood/ucm110591.htm. Updated June 24, 2013. Accessed January 9, 2014.
Last reviewed January 2014 by Michael Woods, MD
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