In the study, Dr. Jean Golding, at the University of Bristol, and colleagues found an association between a low omega-3 fatty acid intake from seafood and an increased risk of high levels of depressive symptoms during pregnancy.

They report the finding in the latest issue of the journal Epidemiology.

The researchers studied 9960 pregnant women. At 32 weeks of pregnancy, the women completed a questionnaire that included questions about mood and the amount of seafood they ate weekly during 1991 and 1992 -- a period when seafood was the main source of omega-3 fatty acids in Britain.

Compared with pregnant women who ate 3 or more servings of seafood per week - the equivalent of more than 1.5 grams of omega-3 fatty acids -- those who ate no seafood were about 50 percent more likely to report symptoms of depression at 32 weeks of pregnancy, the researchers found.

The association between low seafood intake and greater symptoms of depression remained strong even when Golding's team accounted for a variety of factors that might influence the results.

Depression during pregnancy is harmful for both mother and child, Golding and colleagues note in their report. Although common in western countries, depression appears to be virtually absent in countries where people eat a lot of fish.

The researchers call for further investigation into ties between seafood intake and depression in pregnancy, particularly in light of recommendations for pregnant women to limit some seafood consumption due to its mercury content.

"It's possible," they wrote, "that limiting intake in accordance with this advice could increase the risk of maternal depressive symptoms during pregnancy."