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How much fish is safe for pregnant women?

The U.S. Food and Drug Administration and the Environmental Protection Agency are offering new advice for pregnant women about how much fish is safe to eat. The government agencies recommend expectant mothers consume at least 8 ounces and up to 12 ounces (2-3 servings) per week of fish varieties known to be lower in mercury, as a way to support fetal growth and development.

The FDA had not previously set a minimum recommendation for the amount of fish to be eaten each week, although the maximum of 12 ounces a week remains unchanged.

However, the agency says it does not plan to add food labels or signs to inform consumers which fish have the lowest mercury levels and are safest for dinner. Without labels, the draft advice issued Tuesday is unlikely to clear up confusion among shoppers about what seafood is safest for pregnant women, young children and other vulnerable groups.

Consumer groups have sued the agency, saying the warnings over the last decade haven't been clear enough about what fish could pose a risk. Those groups asked for labels on packages or at fish counters.

Some health experts say the risk of mercury poisoning from fish is overstated. But for a decade, the FDA has warned that pregnant or breastfeeding women, those who may become pregnant, and young children avoid certain types of high-mercury fish, such as swordfish, tilefish, king mackerel and shark, because of concern that too much could harm a developing brain.

Fish can absorb small amounts of mercury, a neurotoxin from streams and oceans -- and some larger fish harbor higher levels. But the seafood industry has said the government shouldn't look at mercury by itself, but at the overall benefits of consuming seafood.

"We know that fish and fatty acids are very important for the development of the neurologic system including the brain [and] eyes," Dr. Angela Bianco, associate professor of obstetrics, gynecology and reproductive science at Mount Sinai Hospital in New York City, told CBS News. "Canned tuna is fine; even deep sea tuna, one serving a week would be fine."

Echoing earlier advice, the agencies said pregnant women and children should not eat shark, swordfish, king mackerel and tilefish from the Gulf of Mexico because of the mercury content and advised limiting white albacore tuna to six ounces a week.

The advisory says many of the most commonly-eaten fish are lower in mercury, including salmon, shrimp, pollock, tilapia, catfish, cod, flatfish, haddock and canned light tuna.

The FDA conducted an analysis of more than 1,000 pregnant women in the United States and found that 21 percent of them ate no fish in the previous month, and most of those who did eat fish ate far less than the recommended amount. The seafood industry has said the government shouldn't look at mercury by itself, but at the overall benefits of seafood.

Eight months pregnant with her third child, Jessa Martinez knows a lot about what fish to eat. "I stay away from larger fish," she told CBS News. "I'm a fish lover, so the more fish the better as long as it's safe."

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