Olsen 1992.

Methods	Randomised controlled trial. Olsen 1992 was the main trial with 16 publications. All 16 publications are included in the references to included studies.
Participants	Setting: Denmark. Pregnant women were recruited from the midwife clinic at 30 weeks' gestation. Exluded were women with a history of placental abruption in a previous pregnancy or a serious bleeding episode in the present pregnancy, women who used prostaglandin inhibitors regularly, multiple pregnancies, allergy to fish, and regular intake of fish oil (n = 533).
Interventions	Intervention: 4 x 1 g fish oil capsules daily containing 32% EPA and 23% DHA to provide 1.28 g EPA and 0.92 g DHA. Control group 1: 4 x 1 g capsules of olive oil daily. Control group 2: no supplement. Duration of intervention: 30th week of gestation until delivery.
Outcomes	1. Olsen 1992 reported Primary outcome ‐ pregnancy duration. Secondary outcomes included side effects and complications including postpartum bleeding. 2. Olsen 2008 reported Primary outcome ‐ asthma at 16 years of age. Secondary outcomes ‐ combined outcome of asthma, atopic dermatitis and allergic rhinitis at 16 years of age. Medically diagnosed (from a mandatory registry that recorded diagnoses from hospitals in Denmark) allergy outcomes.
Notes	For this systematic review control groups 1 and 2 were combined to compare with the intervention group (see 'Risk of bias' table).
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote "Women were randomly assigned to the three groups in the ratio 2/1/1. Randomisation was stratified by parity and arranged in balanced blocks of between 8 and 12”.
Allocation concealment (selection bias)	Low risk	Quote "Sealed, opaque envelope for that study number contained a randomisation number that either identified a particular package of oil capsules or showed that the woman should receive no oil supplement".
Blinding of participants and personnel (performance bias) All outcomes	High risk	While group 1 and 2 were blinded, group 3 received no supplement and were therefore unblinded.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Independant evaluation, registry based diagnosis.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Randomised 533 (intervention 266; olive oil 136; and no oil 131). Assessed at 16 years 528 (99%) (intervention 263; olive oil 136; and no oil 129).
Selective reporting (reporting bias)	High risk	Trial registered at ClinicalTrials.gov identifier: NCT01353807. Most of the prespecified outcomes were reported in this trial according to their protocol. However, outcomes of interest to the review are not reported completely. Only limited data were reported on some of the prespecified review outcomes.
Other bias	Low risk	Placebo group and no oil group were combined in the review. Analyses were conducted with the n‐3 LCPUFA supplementation group compared to olive oil control group separately to n‐3 LCPUFA supplementation group compared to no supplement control group, although the direction of effect differed it made little difference to the meta‐analysis.