The health benefits of fish are ever growing. In a recent study of children 6 months to 8 years old, researchers in Great Britain found that pregnant women who ate at least two servings (12 ounces) of fish per week were 52 percent less likely to have a child with low verbal IQ scores. And a Finnish study found that eating fish during pregnancy can reduce a woman's risk of preterm delivery. Many fish are high in healthy fats called omega-3s, which may account, at least in part, for these benefits.
The U.S. Food and Drug Administration and the U.S. Environmental Protection Agency say you can safely eat up to 12 ounces of low-mercury fish a week. Some low-mercury fish that are also rich in omega-3s are salmon, herring, anchovies, caviar, and sardines.
Although many fish are healthy, several can be dangerous to eat. These contain trace amounts of mercury; the metal accumulates in a fish's tissue and is most concentrated in swimmers at the top of the food chain, like sharks, that eat other, smaller fish. For this reason, the FDA and EPA advise pregnant women not to eat swordfish, shark, king mackerel, and tilefish. These may contain enough mercury to harm an unborn baby's developing nervous system -- mercury bypasses the placenta and goes straight to a baby's brain.
The FDA also advises limiting the amount of canned albacore tuna you eat to 6 ounces or less a week. Its mercury content is on average three times that of canned chunk light tuna. Also on the no-go list: game fish such as trout and bass, because they can be contaminated with mercury or other industrial pollutants.
Raw fish, especially shellfish, are potentially dangerous because they can contain harmful microbes that can lead to severe gastrointestinal illness. Smoked seafood like lox is also a no-no unless it's part of a fully cooked dish.
Whatever you're serving, make sure it's thoroughly cooked -- check that the fish is opaque and flakes easily with a fork.