For years, pregnant and nursing women have been warned to limit the amount of fish they eat, because many fish species may contain high levels of mercury, which endangers development in newborns and fetuses. Recently, National Healthy Mothers, Healthy Babies Coalition, a children’s health group challenged the conventional wisdom, they are advising pregnant women and nursing mothers to eat more fish so as to ensure optimal brain development in their babies.

Fearing mercury contamination, many pregnant women eliminate fish from their diet altogether. Researcher are beginning to show that, that may actually harm newborns. (John McConnico for The New York Times) What’s going on here? Currently, the Food and Drug Administration advises pregnant women to limit their weekly seafood consumption to no more than 12 ounces, or about two servings, per week. In addition they recommend staying away from fish that are meat eating (shark, tuna, etc.) as they tend to have higher levels of mercury.

The newest recommendation comes from the National Healthy Mothers, Healthy Babies Coalition, a nonprofit group that focuses on childhood health issues. That group’s scientific advisers say that pregnant women and nursing mothers should eat at least 12 ounces of fish per week. Although both recommendations limit the amount of fish that pregnant women can safely eat to about two servings a week, fears of mercury contamination in seafood have prompted many pregnant women to eliminate fish entirely.

And here’s the issue that pregnant women face: an increasing number of studies indicate that omega-3 fatty acids, found mainly in fish, are essential to brain development in fetuses and newborns. Earlier this year, a report in The Lancet medical journal, concluded that women who had eaten more than 12 ounces of fish per week during pregnancy produced better developed, more intelligent children. “Advice that limits seafood consumption might reduce the intake of nutrients necessary for optimum neurological development,” wrote scientists from the National Institutes of Health and the University of Illinois at Chicago.

“The real problem here are the women who are just eliminating fish from their diet,” said Judy Meehan, executive director of the National Healthy Mothers, Healthy Babies Coalition. “Eating 12 ounces is a very safe, smart move, and nobody is disputing that.’’ While none of the research cited in the coalition’s recommendations has been funded by the fish industry, the coalition is using a grant from the National Fisheries Institute, a seafood industry group, to fund an educational campaign.

For women who want the health benefits but worry about mercury and other toxins, the wisest course is to choose fish with the lowest levels of mercury. A recent report in The Journal of the American Medical Association concluded that the health benefits are likely greatest from such oily fish as salmon, herring and sardines — which are all generally low in mercury anyway. Among the fish to avoid are shark, swordfish, king mackerel and tilefish, all of which may contain high levels of mercury.