Length of Gestation & Risk of Prematurity
Evidence from Epidemiologic Studies
In the 1980s, Scandinavian epidemiologists noted that gestational length and birthweights were increased among women living in the Faroe Islands, compared with Danish women.[34,35] These women were observed to have a high dietary fish intake compared with women living in Denmark, and investigators hypothesized that the prolonged gestational length might be related to intake of fish oil. Potential mechanisms whereby the omega-3 fatty acids found in fish might delay parturition include competitive inhibition of arachidonic acid in the formation of E- and F-series prostaglandins or through antiarrhythmic effects on uterine myometrial activity.
Subsequent observational studies examining the association of fish consumption on length of gestation have yielded conflicting results. A prospective observational study of 8729 women carried out in Aarhus, Denmark, found that diets with low seafood consumption were associated with shorter gestations and increased risk of preterm birth. By contrast, studies in Reykjavik (Iceland), Bristol (UK) and Boston (USA) found no association of fish consumption with gestational length or prematurity. The most recent prospective cohort study carried out in Denmark examined fish consumption in the first two trimesters of pregnancy by means of food frequency questionnaires administered around gestational weeks 16 and 30. In this cohort, women who never consumed fish had significantly shorter gestations and significantly increased risk for preterm birth compared with women who consumed fish at least once weekly.
In a case–control study of omega-3/omega-6 ratios among 37 women delivering preterm (mean gestational age 34 weeks) and 34 control women delivering at term, Reece et al. demonstrated higher levels of arachidonic acid (an omega-6 precursor) and docosapentaenoic acid (an omega-6 fatty acid) in women delivering preterm than in women delivered at term. In addition, maternal plasma omega-3:omega-6 ratio at 34 weeks was shown to be higher in women delivering at term than those delivering preterm.
Evidence from Clinical Trials
A number of randomized or quasi-randomized trials carried out since the 1930s have explored potential benefits of fish oil or cod liver oil use during pregnancy on length of gestation and prevention of prematurity. The earliest study, the People's League of Health trial, carried out among 5000 pregnant women in London (UK) between 1938 and 1939, used alternate day allocation to assign women at approximately 20 weeks' gestation to either vitamins, minerals and halibut liver oil, or placebo.[43,44] Reductions in births before 40 weeks of gestation, as well as the incidence of preeclampsia, were noted in the supplemented group. While of considerable historical interest, this study would not meet modern investigational standards.
There have been three recently published systematic reviews that have summarized the findings of the randomized, controlled trials of fish oil supplementation on gestational length and preterm births. The Cochrane review of marine (fish or algae) oil supplementation in pregnancy combined three trials, including 1621 participants, that reported on the effects of supplementation on gestational length. The reviewers found that supplementation with marine oil resulted in prolongation of gestation by 2.6 days, a prolongation that was statistically significant for singleton gestations but not for twin gestations. To address the question of whether marine oil might prevent preterm births, the authors combined five trials with 1916 participants; this analysis did not reveal any decrease in preterm births at less than 37 weeks, but analysis of data from two trials with 860 participants revealed reduction in early preterm births under 34 weeks (relative risk [RR]: 0.69; 95% CI: 0.47–0.99). In the two studies examining post-term gestations, there was a trend to more post-term gestations among women receiving marine oil, but this trend was not statistically significant.
Expert Rev of Obstet Gynecol. 2010;5(1):125-138. © 2010
Cite this: Role of Omega-3 Fatty Acids in Maternal, Fetal, Infant and Child Wellbeing - Medscape - Jan 01, 2010.