Fish oil supplementation and duration of pregnancy

Nutrition Research Newsletter, May, 1992

Women in the Faroe Islands (a group of Danish islands in the North Atlantic) have pregnancies of longer duration than those of women in most other parts of the world, and their infants have high birth weights. It has been hypothesized that a high intake of fat rich in n-3 fatty acids (from fish and whales) prolongs gestation in these women, perhaps through effects on prostaglandin formation. To test this hypothesis, researchers in Aarhus, Denmark, conducted a randomized, controlled trial of the effect of fish oil supplementation on pregnancy duration.

Between November 1989 and July 1990, 533 healthy Aarhus women in the 30th week of pregnancy were randomly assigned to receive a fish oil supplement containing 2.7 g n-3 fatty acids per day, an olive oil placebo, or no supplement for the remainder of their pregnancies. Average intake of n-3 fatty acids in the fish oil group was increased by a factor of about ten.

Pregnancies in the fish oil group were on average 4.0 days longer than those in the olive oil group (a statistically significant increase) and birth weights were 107 g higher. These differences are similar to those between women in the Faroe Islands and in Denmark (3.7 days and 100 g). The effect of fish oil supplementation was strongest in women who had low fish consumption at entry to the study, suggesting that the effect of fish oil can reach a saturation level. There was a trend toward greater blood loss at delivery in the fish oil group, but there were no significant differences between the groups in other complications of childbirth.

The authors conclude that "fish-oil supplementation in late pregnancy seems to delay delivery, without affecting the continued growth of the fetus or impairing the process of parturition." The findings suggest the possibility that n-3 fatty acids might represent "an easy and cheap intervention to prevent preterm delivery." Further studies are needed, particularly in women at high risk of preterm delivery, to determine whether fish oil is safe and effective for this purpose.

Sjurdur F Olsen et al, Randomised Controlled Trial of Effect of Fish-Oil Supplementation on Pregnancy Duration, Lancet 339(8800):1003-1007 (25 Apr 1992) [Correspondence: Dr Sjurdur F Olsen, Institute of Epidemiology and Social Medicine, University of Aarhus, Hoegh-Guldbergs Gade 8, DK-8000 Aarhus C, Denmark]