Furuhjelm 2009.

Methods	Randomised controlled trial. Furuhjelm 2009 was the main trial with 6 reports. All 6 publications are included in the references to included studies.
Participants	Setting: Sweden. 145 pregnant women who were at high risk of having a baby with atopy were recruited through antenatal care clinics during a 2‐year period in 2003–2005. Women were considered at high risk if they, or their husband or an older child had current or previous allergic symptoms, i.e. bronchial asthma diagnosed by a doctor, atopic eczema, allergic food reactions, itching and running eyes and nose on exposure to pollen, pets or other known allergens.
Interventions	Intervention: Women took 9 500 mg capsules a day containing 35% EPA, and 25% DHA, to provide 1.6 g of EPA and 1.1 g of DHA, n = 70. Control: 9 soy oil capsules a day, containing 58% LA to provide 2.5 g LA/day and 6% ALA to provide 0.28 g ALA/day, (n.=.75). Duration of intervention: 25th week of gestation to delivery, encouraged to continue during lactation (average 3 to 4 months).
Outcomes	1. Furuhjelm 2009 reported Medically diagnosed allergy outcomes at 3, 6 and 12 months of age including: IgE antibody analysis, food allergy and eczema. Food allergy was defined as gastrointestinal symptoms, hives, aggravated eczema or wheeze following ingestion of egg or milk in the presence of detectable IgE antibodies or a positive SPT towards the particular food. Recovery from symptoms after elimination of the particular food from the diet and reoccurrence after ingestion of the food was required for the diagnosis. IgE‐associated eczema was characterised as reoccurring and itching eczematous, lichenified or nummular dermatitis according to the criteria modified by Oranje 1995 in the presence of detectable IgE antibodies or positive SPT towards egg, milk or wheat. 2. Furuhjelm 2011 reported Medically diagnosed allergy outcomes at 2 years of age including: food allergy, eczema, allergic rhinitis, asthma and any allergies with or without IgE associated.
Notes	The trial was supported financially by the Medical Research Council of Southeast Sweden (FORSS), The Östergötland County Council, The Ekhaga Foundation, Swedish Asthma and Allergy Association, The Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS), The Swedish Society of Medicine and Glaxo Smith Kline, Sweden.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The mothers were randomly allocated to dietary supplementation either with Ѡ‐3 fatty acids or placebo".
Allocation concealment (selection bias)	Low risk	Quote: "Producer performed the block randomisation". We interpreted this as central allocation.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "Active and placebo capsules could not be distinguished from each other".
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "The research nurses, the paediatricians and the person performing the laboratory analyses were blinded during the intervention and follow‐up".
Incomplete outcome data (attrition bias) All outcomes	High risk	Randomised n = 145 (70 intervention, 75 control). 25 did not complete the requested 15 week intervention period (16, 23% treatment and 9, 12% placebo) and were excluded from the analysis, 1 withdrew post delivery, 2 not followed as moved before 6/12 follow up (group not stated). Total 28 (19%) not included in analysis, 117 included (81%). SPT 117 (81%) at 6 months, 115 (79%) at 12 months. Medically diagnosed allergy outcomes were reported on n = 117 (81%) (fish oil group n = 52 (74%) and control group n = 65 (87%), at 6 months and at 1 year of age. Medically diagnosed allergy outcomes were reported on n = 119 (82%) (fish oil group n = 54 (77%) and control group n = 65 (87%), at 2 years of age.
Selective reporting (reporting bias)	Low risk	Trial registered at ClinicalTrials.gov identifier: NCT00892684. Prespecified outcomes were reported in this trial according to their protocol. Outcomes of interest to the review are reported.
Other bias	Low risk	No obvious risk of other bias.