Background: Long-chain omega-3 polyunsaturated fatty acids are thought to be important for fetal neurodevelopment. Animal studies suggest that a deficiency of omega-3 fatty acids may lead to behavioural or cognitive deficits. As oily fish is a major dietary source of omega-3 fatty acids, it is possible that low intake of fish during pregnancy may have adverse effects on the developing fetal brain.

Methods: We used the Strengths and Difficulties Questionnaire and the Wechsler Abbreviated Scale of Intelligence to assess behavioural problems and intelligence in 217 nine-year-old children. The mothers of these children had participated in a study of nutrition during pregnancy during which fish intake was assessed in early and late gestation.

Results: Children whose mothers had eaten oily fish in early pregnancy had a reduced risk of hyperactivity compared to those whose mothers did not eat oily fish: OR .34, 95% CI .15 to .78, after adjustment for potential confounding factors. Children whose mothers had eaten fish (whether oily or non-oily) in late pregnancy had a verbal IQ that was 7.55 points higher (95% CI .75 to 14.4) than those whose mothers did not eat fish. There were, however, no significant associations between fish intake in pregnancy and other behavioural problems or full-scale and performance intelligence, after adjustment for potential confounding factors.

Conclusions: Although maternal fish intake in pregnancy was associated with hyperactivity scores and verbal IQ in children, in general, how much fish women ate during pregnancy appeared to have little long-term relation with neurodevelopmental outcomes in their child.