Higher birthweight has been associated with a lower risk of diseases later in life, add the authors, so mothers that take cod liver oil might help protect their children against a number of adult health conditions.
Cod liver oil is still popular in north European countries, offering vitamin D during winter months and valuable omega-3 polyunsaturated fatty acids.
Icelandic birthweights are among the highest in the world so a team from the Public Health Institute of Iceland estimated marine food and cod liver oil intake in 435 healthy pregnant women using a semi-quantitative food frequency questionnaire covering food intake together with lifestyle factors for the previous three months.
The women, observed in free-living conditions, had experienced no complications prior to the study start date. They filled out the questionnaires between 11 and 15 weeks and between 34 and 37 weeks of gestation.
The researchers report that 14 per cent of the study population used liquid cod liver oil in early pregnancy and these women gave birth to heavier babies, even after adjusting for the length of gestation and other confounding factors.
After adjusting for confounding variables, healthy women were 11 times more likely to give birth to an infant weighing 4,500 g or more if they used liquid cod liver oil. The authors attributed these findings to the increased intake of omega-3 fatty acids from the liquid cod liver oil.
Women taking liquid cod liver oil were also significantly older and less likely to be delivering their first child, found the report in the April issue of the British Journal of Obstetrics and Gynecology (vol 112, issue 4, pp424-9).
The findings counter a study published by researchers at Bristol University in the UK last year. Although they found mothers-to-be who ate fish during the later stages of pregnancy were less likely to have a very small baby, there was no link between fish consumption and average birthweight once other factors were taken into account.