Eating one serving of fish a week during pregnancy may lower a mother-to-be's anxiety, a new Brazilian study finds.

Findings showed that pregnant women who never or rarely ate dark or oily fish (salmon and tuna, for example) were 53 per cent more likely to experience high levels of anxiety in their third trimester compared with women who ate fish at least once a week.

Vegetarian women were also 25 per cent more likely to have anxiety compared with women who had consumed some fish and meat. Researchers from the Federal University of Pelotas recruited 9,500 women for the study, grouping the women based on their dietary patterns. At 32 weeks of pregnancy, the women completed questionnaires about their anxiety levels.

"In order to have a healthy pregnancy, women need to follow a healthy diet, and not something special for pregnancy," said study author Juliana Vaz, according to LiveScience on Wednesday. She recommends a diet rich in whole grains, vegetables, meat, poultry, and fish.

As to why fish had an effect on anxiety isn't clear but the researchers suggest it could be due to omega-3 fatty acids. The study appeared online last week in the journal Plos One.

But some experts warn that eating fish during pregnancy could increase your baby's exposure to mercury. Consider bypassing larger fish, such as shark and swordfish, which can contain higher levels of mercury, in favor of anchovies, salmon, herring, and sardines, advises Dr. Roger W. Harms, a pregnancy specialist at the Mayo Clinic in the US.

Access the study: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0067671