During pregnancy, women are warned to closely monitor their diet and limit or abstain from the consumption of alcohol and fish. The nutritious and nutrient-dense food, which contains some unhealthy contaminants, has long been a cause for concern for doctors who have limited consumption to no more than two 6-ounce servings per week. Now, the Food and Drug Administration (FDA) advises pregnant women eat more fish, necessary for growth and development of the fetus.

"[E]merging science now tells us that limiting or avoiding fish during pregnancy and early childhood can mean missing out on important nutrients that can have a positive impact on growth and development, as well as on general health," said Stephen Ostroff, the FDA's acting chief scientist, in the FDA news release. It is known that the benefits of seafood are greater than the risks, and there are many types of low-mercury seafood that are good sources of omega-3 fatty acids that won’t endanger the fetus.

FDA and Environmental Protection Agency (EPA) decade-old guidelines say that children, women who are pregnant, and women who are trying to become pregnant should consume no more than 12 oz. (340 grams) of low-mercury fish per week. Fish with high mercury levels should be avoided, and high mercury fish should be kept to only three 6-ounce servings per month. This echoes the 2010 Dietary Guidelines for Americans that recommends 8 to 12 oz. of seafood a week for pregnant women, or about two average meals.

Mercury in seafood isn’t a concern for most adults, says the Mayo Clinic, but special precautions do apply if a woman is pregnant or is planning to become pregnant. Regularly eating fish high in mercury can lead to the substance accumulating over time. Therefore, too much mercury in the bloodstream can potentially be detrimental to a baby’s developing brain and nervous system.

The FDA’s updated draft advice comes after the agency did an analysis of more than 1,000 pregnant women in the U.S. and found 21 percent of them ate no fish in the previous month. Those who did eat fish were found to consume less than the recommended amount. This statistic may be attributed to the agency’s failure to set a minimum amount of fish consumption for this population group.

Researchers have contested with the proposed FDA limits for years, citing a study that found no negative effects for women who did consume more seafood than the FDA-approved guidelines. The 2003 study published in the journal The Lancet, investigated a large cohort of children from before birth to nine years of age and noted there were no detectable adverse effects in a population consuming 10 times the average amount of fish a U.S. citizen eats. The pregnant women ate a wide variety of ocean fish.

While researchers and public health agencies debate about mercury consumption during pregnancy, the FDA hopes the advice will become second nature to pregnant women. The FDA has "begun the process of setting the record straight that fish should be a pregnancy staple,” said Jennifer McGuire of the National Fisheries Institute, the Associated Press reported. The agency, along with the EPA will take public comments, seek the advice of the FDA's Risk Communication Advisory Committee, and conduct focus groups before making the advice final.

The draft aims to give consumers more information about the levels of omega-3 fatty acids and mercury in certain fish, but also to allow shoppers to determine which fish are the best. Although the agency urges pregnant women to eat more fish, there won’t be any labels or signs to let them know which fish have lower mercury levels, or are the safest for dinner.

To be a saavy fish consumer, here’s a list of the fish with the least, moderate, high, and highest mercury levels, courtesy of Natural Resources Defense Council

Least Mercury

Enjoy these fish:

Anchovies, Butterfish, Catfish, Clam, Crab (Domestic), Crawfish/Crayfish, Croaker (Atlantic), Flounder, Haddock (Atlantic), Hake, Herring, Mackerel (N. Atlantic, Chub), Mullet, Oyster, Perch (Ocean), Plaice, Pollock, Salmon (Canned), Salmon (Fresh), Sardine, Scallop, Shad (American), Shrimp, Sole (Pacific), Squid (Calamari), Tilapia, Trout (Freshwater), Whitefish, Whiting

Moderate Mercury

Eat six servings or less per month:

Bass (Striped, Black), Carp, Cod (Alaskan), Croaker (White Pacific), Halibut (Atlantic), Halibut (Pacific), Jacksmelt (Silverside), Lobster, Mahi Mahi, Monkfish, Perch (Freshwater), Sablefish, Skate Snapper, Tuna (Canned chunk light), Tuna (Skipjack), Weakfish (Sea Trout) 

High Mercury

Eat three servings or less per month:

Bluefish, Grouper, Mackerel (Spanish, Gulf), Sea Bass (Chilean), Tuna (Canned Albacore), Tuna (Yellowfin)

Highest Mercury

Avoid eating:

Mackerel (King), Marlin, Orange Roughy, Shark, Swordfish, Tilefish, Tuna (Bigeye, Ahi)