Abstract: Eight trials involving 3366 women and their 3175 children were included in the review. In these trials, women were supplemented with n-3 LCPUFA during pregnancy (five trials), lactation (two trials) or both pregnancy and lactation (one trial). All trials randomly allocated women to either a n-3 LCPUFA supplement or a control group. The risk of bias varied across the eight included trials in this review with only two trials with a low risk of selection, performance and attrition bias. N-3 LCPUFA supplementation showed a clear reduction in the primary outcome of any allergy (medically diagnosed IgE mediated) in children aged 12 to 36 months (risk ratio (RR) 0.66, 95% confidence interval (CI) 0.44 to 0.98; two RCTs; 823 children), but not beyond 36 months (RR 0.86, 95% CI 0.61 to 1.20; one RCT, 706 children). For any allergy (medically diagnosed IgE mediated and/or parental report), no clear differences were seen in children either at 12 to 36 months (RR 0.89, 95% CI 0.71 to 1.11; two RCTs, 823 children) or beyond 36 months of age (RR 0.96, 95% CI 0.84 to 1.09; three RCTs, 1765 children). For the secondary outcomes of specific allergies there were no clear differences for food allergies at 12 to 36 months and beyond 36 months, but a clear reduction was seen for children in their first 12 months with n-3 LCPUFA (both for medically diagnosed IgE mediated and medically diagnosed IgE mediated and/or parental report). There was a clear reduction in medically diagnosed IgE-mediated eczema with n-3 LCPUFA for children 12 to 36 months of age, but not at any other time point for both medically diagnosed IgE mediated and medically diagnosed IgE mediated and/or parental report. No clear differences for allergic rhinitis or asthma/wheeze were seen at any time point for both medically diagnosed IgE mediated, and medically diagnosed IgE mediated and/or parental report. There was a clear reduction in children's sensitisation to egg and sensitisation to any allergen between 12 to 36 months of age when mothers were supplemented with n-3 LCPUFA. In terms of safety for the mother and child, n-3 LCPUFA supplementation during pregnancy did not show increased risk of postpartum haemorrhage or early childhood infections. Overall, there is limited evidence to support maternal n-3 LCPUFA supplementation during pregnancy and/or lactation for reducing allergic disease in children. Few differences in childhood allergic disease were seen between women who were supplemented with n-3 LCPUFA and those who were not.

Plain-language summary: In this review of randomised controlled studies, we evaluated the effects of adding marine omega-3 fatty acids to women’s diets during pregnancy or lactation on allergic diseases in their children. We analysed eight trials that involved 3366 women and 3175 children. The women were randomly assigned to receive a marine omega-3 supplement (as fish oil capsules, or added to foods) or no treatment during pregnancy (five trials), during breast feeding (two trials) or both pregnancy and breast feeding (one trial). Overall, the methodological quality of the trials varied, with only two trials being at low risk of bias. Overall, the results showed little effect of maternal marine omega-3 supplementation during pregnancy and/or breast feeding for the reduction of allergic disease in the children. However there were reductions in some outcomes such as food allergy during the baby's first year and eczema with marine omega-3 supplementation in women with a baby at high risk of allergy. Currently, there is not enough evidence to say that omega-3 supplements from marine origin during pregnancy and/or breast feeding for mothers will reduce allergies in their children. In terms of safety for the mother and child, omega-3 fatty acids supplementation from marine origin during pregnancy did not show increased risk of excessive bleeding after the baby was born (postpartum haemorrhage) or early childhood infections.