by Karen Schroeder, MS, RD
Some fish contain high levels of methylmercury, a form of the element mercury. If a pregnant woman consumes methylmercury regularly, it may harm her unborn child's developing nervous system. Therefore, there are certain types of fish that you should avoid if you are pregnant or breast feeding. However, this doesn't mean that you have to banish all fish—an excellent source of protein, minerals, and healthful fatty acids—from your diet.
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
methyl mercury, which is a toxic form. As fish feed on plants and organisms in
the water, they absorb methyl mercury. This methyl mercury can damage the
nervous system of a developing child.
Large fish that feed on other fish and live long lives accumulate high levels of
methyl mercury in their bodies. These are the fish most likely to cause adverse
effects because of their high methyl mercury concentration. The U.S. Food and
Drug Administration (FDA) recommends that pregnant women as well as nursing
mothers and young children avoid the following large fish that contain high
levels of methyl mercury:
- Shark
- Swordfish
- King mackerel
- Tilefish
What about other types of fish?
Tuna, salmon, crab, lobster... all other types of fish and shellfish are safe for pregnant women as long as they eat a variety of types of fish, and eat them in moderation. A safe level is 12 ounces of cooked fish per week. A serving of fish is typically 3 to 6 ounces, but be aware that portion sizes in restaurants tend to be larger.
There are also certain types of fish that have lower-than-normal levels of mercury. This may vary depending on where the fish was caught. Check with your local health department regarding the mercury levels of fish in your area.