The research, published on-line ahead of print in the journal Environmental Health Perspectives (doi: 10.1289/ehp.9329), has already been picked up by many mainstream news publications, including New Scientist, and could reignite the debate about whether the benefits of fish consumption may outweigh the risks.
Consumers have been receiving mixed messages with some claiming that the benefits of fish consumption, like omega-3, protein, and essential vitamins and minerals content outweigh the risks posed by pollutants such a methyl mercury, dioxins, and polychlorinated biphenols (PCBs).
The situation is particularly sensitive for pregnant women, with such pollutants reported to damage the development of babies.
But a diet rich in the omega-3 fatty acid, docosahexaenoic acid (DHA), during pregnancy and breastfeeding is thought to support healthy pregnancies as well as the mental and visual development of infants.
The Pregnancy Outcomes and Community Health (POUCH) study, by researchers at Harvard University and Michigan State University, recruited 1,024 women between their 15th and 27th week of pregnancy. Dietary consumption of fish was evaluated by in-person interviews and self-administered questionnaires, while hair sample were taken in order to establish methyl mercury levels in the mothers.
Lead author Fei Xue reported that women with higher intake of fish consumption were more likely to have higher methyl mercury levels, and women who gave birth prematurely were more likely to be in the top ten per cent of methyl mercury hair levels.
"Our study is the first to report an association between delivery at less than 35 weeks' gestation and maternal hair mercury levels at or above 0.55 [parts per million]," she wrote.
The average mercury level was 0.29 ppm.
The authors stressed however that only 44 of the 1,024 women in the study (about four per cent of the study population) actually gave birth prematurely and called for more studies to test the association.
While other studies have reported links between mercury exposure during faetal development and cognitive problems, the science remains inconsistent. Indeed, back in February a panel of experts at the annual meeting of the American Association for the Advancement of Science said that the benefits of eating seafood continue to outweigh the risks.
During the meeting, Phil Davidson from the University of Rochester Medical School, reported that a ten-year study of over 700 children in the Seychelles Islands, where women average 12 meals of fish a week, showed no cognitive defects that can normally be seen from mercury absorption.
Michael Morrissey from Oregon State Universitys Seafood Laboratory said at the time that pregnant women should stick with current FDA recommendations of about 12 ounces (340 grams) per week. The rest of the population should be eating fish four to seven times per week.