More seafood eaten in pregnancy shown to produce brainier babies

Pregnant women now have something else to worry about - whether they are eating too little, or too much, seafood to give their unborn babies the best start in life.

Research published in The Lancet attempts to settle a dispute that has divided British and US scientists over whether eating fish benefits or damages the developing brain of a foetus.

Fish absorb mercury, a heavy metal that pollutes the seas, which can harm brain development. However, fish also contains omega 3 fatty acids and other nutrients essential to the developing brain. Official US Government advice is for pregnant women to limit their consumption of all seafood, including white fish, oily fish and shellfish, to no more than 12 ounces (340 grams) a week, in order to limit their exposure to mercury.

In the UK, the Food Standards Agency takes a less stringent line advising expectant mothers to avoid shark, swordfish and marlin and to limit consumption of tuna. Those are the fish with the highest levels of mercury, because of their species and the level of pollution in the seas in which they swim.

The new research into children's behaviour and intelligence suggests that instead of protecting the unborn baby, women who follow US advice or cut fish out of their diet altogether may miss out on nutrients that are vital to the brain's development - and so unwittingly harm their children. The findings are taken from a study of almost 9,000 British families taking part in the Children Of The 90s project at the University of Bristol.

Joseph Hibbeln from the US National Institutes of Health, and the Bristol scientists, including Professor Jean Golding, compared the amount of fish eaten by pregnant mothers with the development and behaviour of their offspring up to the age of eight.

Women from socially-advantaged backgrounds were more likely to include fish in their diet but even after adjusting for 28 different factors - such as social class, or whether the mother breastfed - there were significant differences apparent in the children's development.

Mothers who ate more seafood than was considered to be safe according to US guidelines had children who were more advanced. They had higher IQs, better social skills, were more communicative and more physically accomplished.

Those children whose mothers had eaten no fish performed worse on all the same measures.

Dr Hibbeln said: "We have found that when women had low levels of seafood consumption, the outcome is exactly the opposite of what was assumed by the United States Advisory. Unfortunately, the advice appears to have had the unintended consequence of causing harm in a specific developmental domain - verbal development - where protection was originally intended.

"We recorded no evidence to lend support to the warnings of the US advisory that pregnant women should limit their seafood consumption.

"In contrast, we noted that children of mothers who ate small amounts, 340g per week, of seafood were more likely to have suboptimum neurodevelopmental outcomes than children of mothers who ate more seafood than the recommended amounts."

The Royal College of Midwives welcomed the research. RCM education and research manager Sue Macdonald said: "Midwives are very aware of the importance of advising pregnant women and their families about the added benefits of eating fish."

The research follows a study published earlier this week which suggested that women who do not breast feed their babies reduce their chances of climbing the social ladder.