Few studies have explored whether fetal exposure to these fatty acids may encourage the inception of asthma and allergies in children, noted the scientists in the Journal of Allergy and Clinical Immunology. Allergic diseases in youngsters have dramatically increased in western countries over the last 20 to 30 years, and they are often attributed to changes in lifestyle, such as diet.
To investigate whether prenatal consumption of omega-3 and 6 could contribute to an imbalance that might lead ultimately to the airway inflammation involved in asthma, the researchers - led by Dr. Seif Shaheen from King's College, London - studied thousands of blood samples obtained from women during late in pregnancy, as well as umbilical cord blood samples.
They also measured the associations between omega-3 and 6 fatty acids and wheezing at 30 and 42 months and with eczema at 18 to 30 months, and questioned mothers about wheezing and eczema in their children.
Initial evidence suggested there was a positive association between omega-6 fatty acids and wheezing, and a negative link between omega-3 products and wheezing. However, after adjusting the data to take into account other risk factors, the scientists inferred there were no significant differences. They found that this was also the case for eczema.
The researchers therefore concluded that: "It seems unlikely that fetal exposure to omega-6 and omega-3 fatty acids is an important determinant of early childhood wheezing and atopic disease".
These findings were in partial contrast to those presented at the American Thoracic Society International Conference in Orlando by the University of Southern California in May. They suggested that while mothers who ate fish rich in omega-3 were helping to protect their child against developing asthma, omega-6 rich food eaten during pregnancy made children twice as likely to develop asthma.
"Fish sticks are deep-fried, and they contain omega-6 fatty acids, which encourage inflammation of the airways," said study co-author Frank Gilliland, professor of preventive medicine at the Keck School of Medicine at the University of Southern California in Los Angeles.
However oily fish contain omega-3 fatty acids, which appear to be anti-inflammatory, and lead to the reduced potential for developing asthma and allergies, he said.
The study found that children whose mothers with asthma ate oily fish during pregnancy were 71 per cent less likely to develop asthma on average; the more oily fish a woman ate, the less likely her child was to develop asthma.
Children with non-asthmatic mothers did not benefit from having their mother eat oily fish during pregnancy.
"A family history of asthma is a very strong risk factor for a child developing asthma," Dr Gilliland said. "It appears that oily fish interacts with the genes involved in the predisposition to develop asthma, and somehow reduces the risk."
The prevalence of asthma is increasing in all western populations and diet is being increasingly investigated as a factor in this increase. From 1980 to 1995, the prevalence of asthma increased 5 per cent each year among American children, and the death rate for children 19 years of age and younger increased by 78 per cent between 1980 and 1993, according to the Asthma and Allergy Foundation of America.