Jamilian 2017.

Methods	RCT (4 arms, see below)
Participants	140 women randomised Inclusion criteria: women 18‐40 years; without prior diabetes; diagnosed with GDM by 1‐step 2‐hour 75‐g OGTT at 24‐28 weeks’ gestation referred to Kosar Clinic in Arak, Iran. GDM was diagnosed according to the ADA guidelines: those whose plasma glucose met 1 of the following criteria were considered as having GDM: FPG ≥ 92 mg/dL, 1‐hour OGTT ≥ 180 mg/dL, and 2‐hour OGTT ≥ 153 mg/dL. Exclusion criteria: taking vitamin D and/or omega‐3 fatty acid supplements; taking insulin; placental abruption; PE; hypothryroidism and hyperthyroidism; smokers; those with kidney or liver disease Setting: Kosar Clinic, Arak, Iran; women were recruited from March 2016 to July 2016
Interventions	SUPPLEMENTATION + OTHER AGENT: omega‐3 versus omega‐3 + vitamin D versus vitamin D versus placebo Group 1: omega‐3 fatty acids (2000 mg; 720 mg EPA and 480 mg DHA per day) as 2 capsules (produced by Zahravi Pharmaceutical Company, Tabriz, Iran): n = 35 randomised (n = 32 completed study) Group 2: omega‐3 fatty acids (2000 mg; 720 mg EPA and 480 mg DHA per day) as 2 capsules plus vitamin D (50,000 IU every 2 weeks): n = 35 randomised (and completed study) Group 3: vitamin D (50,000 IU every 2 weeks) plus omega‐3 placebo capsules: n = 35 randomised (and completed study) Group 4: no supplement (placebo) as 2 capsules that were indistinguishable in colour, shape, size, and packaging, smell, and taste from the vitamin D and omega‐3 fatty acids capsules: n = 35 randomised (32 completed study) Timing of supplementation: 6 weeks (start 24‐28 weeks' gestation) DHA + EPA dose/day: high: 480 mg DHA + 720 mg EPA
Outcomes	Women/birth: insulin metabolism (primary); lipid concentrations (secondary)
Notes	No outcomes could be included in this review. Funding: grant from the Vice‐Chancellor for Research, AUMS (no.1394.373) Declarations of interest: none declared
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Random sequence generation was ensured using a computer‐generated random numbers table.
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "appearance of placebo capsule was indistinguishable in color, shape, size, and packaging, smell, and taste from Vitamin D and omega‐3 fatty acids capsules"; considering the nature of intervention and placebo, participants and personnel could have been effectively blind to group assignments throughout the trial.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported
Incomplete outcome data (attrition bias) All outcomes	Low risk	140 women were randomised, 35 each to: placebo; vitamin D; omega‐3; and vitamin D + omega‐3. A total of 6 women (3 placebo group, 3 omega‐3), were lost to follow‐up, leaving 134/140 (97%) women randomised in the data collection. The difference in the proportions of randomised women included in the data collection was marginal: 100% of women in the vitamin D and vitamin D + omega 3 groups; and 91% of the women in the remaining 2 groups.
Selective reporting (reporting bias)	Unclear risk	Insufficient information for confident assessment
Other bias	Low risk	Baseline characteristics similar; no obvious other bias identified