In this study, researchers from Bristol University and the US National Institutes of Health questioned 11,875 pregnant women on their fish and seafood consumption. They then looked at the social and communication skills of the children, as well as hand-eye co-ordination and total IQ, up to the age of eight years.

Eating less than 12oz (340g) of fish and seafood a week was associated with a 48% increased risk of children being in the lowest group for verbal intelligence. Low fish and seafood intake During Pregnancy was also associated with increased risk of poorer behaviour, motor, communication and social development scores. The researchers therefore concluded, the lower the consumption of fish, the higher the risk of poorer scores on the neurodevelopmental tests.

Prior to the study by Lancet, a previous paper by the Avon Longitudinal Study Group showed that omega-3 fatty acids contained in fish, particularly oily fish, were associated with boosting children's future brain power and social skills. This study had only looked at children up to the age of three or four whilst the Lancet looked at older children suggesting the benefits were more long-terms than first thought.

However, there have still been concerns raised about the amount and type of fish and seafood that pregnant women should eat. The Food Standards Agency have advised that pregnant women should eat one or two portions of oily fish a week and that they should avoid certain types of fish, including shark and marlin, or lots of tuna, because of the risks to the developing foetus associated with mercury.

Professor Jean Golding, emeritus professor of paediatric and perinatal Epidemiology at the University of Bristol, and head of the study, said women should follow the FSA advice and eat a mixture of different types of fish. Oily fish, the most widely available source of omega-3 fatty acids, that women should eat include salmon, mackerel, pilchards and sardines.

In the UK, pregnant women are advised not to eat more than two tuna steaks a week (weighing about 140g cooked or 170g raw) or four medium-size cans of tuna a week (with a drained weight of about 140g per can) because of the levels of mercury. Seeds such as flax, pumpkin and hemp are good sources of omega-3 for vegetarians, but large quantities need to be consumed to gain the same effect.