Participant attrition and perinatal outcomes in prenatal vitamin D-supplemented gestational diabetes mellitus patients in Asia: A meta-analysis

Table 1 Salient features of the reviewed trials

Ref.	Design	Participants	Interventions	Outcomes
Jamilian et al[37], 2016	Randomized, double-blind, placebo-controlled clinical trial; Intervention arms: Two; Single-centered trialTrial duration: 6 wk. Trial conducted in: Iran; Obtained ethical clearance and participant consent. Funding information provided. Clinical trial registration number: IRCT201509115623N52	Participants diagnosed with GDM (used ADA criteria); 60 participants randomized into different treatment arms (vitamin D3 and evening primrose oil: n = 30, placebo: n = 30); Mean age of participants: -Vitamin D3 and evening primrose oil receiving group: 28.4 ± 6.2 yr; -Placebo receiving group: 29.6 ± 4.3 yr	Two intervention arms: (1) 1000 IU of vitamin D and 1000 mg of evening primrose oil daily for 6 wk; and (2) Placebo	Attrition from vitamin D supplemented arm: n = 3; Other outcomes reported: Fasting plasma glucose
Jamilian et al[17], 2017	Randomized, double blinded, placebo-controlled clinical trial; Intervention arms: four; Single centered trial; Trial duration: 6 wk. Trial conducted in: Iran; Obtained ethical clearance and participant consent. Funding information provided. Clinical trial registration number: IRCT201605135623N78	Participants diagnosed with GDM (used ADA criteria); 140 participants randomized into different treatment arms (vitamin D and omega-3 fatty acid receiving group: n = 35, vitamin D receiving arm: n = 35, omeag-3 fatty acid receiving arm: n = 35, placebo receiving arm: n = 35); Mean age of participants: -Vitamin D and omega-3 fatty acid receiving group: 31.2 ± 4.3 yr; -Vitamin D receiving group: 31.5 ± 7.0 yr; -Omega-3 receiving group: 30.7 ± 3.5 yr; -Placebo receiving group: 30.7 ± 4.1 yr	Four intervention arms: (1) Vitamin D and omega-3 fatty acid: 50000 IU of vitamin D two weekly and 1000 mg omega-3 fatty acid twice daily; (2) Vitamin D: 50000 IU vitamin D every 2 wk; (3) Omega-3 fatty acid: 1000 mg omega-3 fatty acids two times a day; and (4) Placebo	No attrition from vitamin D supplemented arm; Other outcomes reported: Fasting plasma glucose
Jamilian et al[33], 2019a	Randomized, double-blind, placebo-controlled; Intervention arms: 3; Trial conducted in: Iran; Single centered trial; Trial duration: 6 wk; Obtained ethical clearance and participant consent. Funding information provided. Trial ID: IRCT201706075623N119	Participants diagnosed with GDM (used ADA criteria); 90 participants randomized into different treatment arms (probiotic arm: n = 30, vitamin D and probiotic arm: n = 30, placebo arm: n = 30); Mean age of participants: -Probiotic arm: 31.2 ± 5.9 yr; -Vitamin D and probiotic arm: 28.9 ± 6.1 yr; -Placebo arm: 29.9 ± 3.7 yr	Three intervention arms: (1) Probiotic: 8 × 109 CFU/g; (2) Vitamin D3 (50,000 IU) every 2 wk plus 8 × 109 CFU/g probiotic; Placebo	No attrition from vitamin D supplemented arm; Other outcomes reported: (1) Newborn hyperbilirubinemia; (2) Newborn hospitalization; (3) Macrosomia; and (4) Cesarean section. Fasting plasma glucose
Jamilian et al[36], 2019b	Randomized, double-blind, placebo-controlled. Intervention arms: 2; Trial conducted in: IranSingle centered trialTrial duration: 6 wkObtained ethical clearance and participant consent. Funding information provided.Trial ID: IRCT201704225623N109	Participants diagnosed with GDM (used ADA criteria); 60 participants randomized into different treatment arms (vitamin D-magnesium-zinc-calcium arm: n = 30, placebo arm: n = 30). Mean age of participants: -Vitamin D-magnesium-zinc-calcium arm: 27.7 ± 4.0 yr; -Placebo arm: 29.1 ± 4.1 yr	Two intervention arms: (1) Vitamin D (200 IU) along with 100 mg magnesium, 4 mg zinc, 400 mg calcium twice daily; and (2) Placebo	No attrition from vitamin D supplemented armOther outcomes reported: (1) Newborn hyperbilirubinemia; (2) Newborn hospitalization; (3) Macrosomia; and (4) Cesarean section. Fasting plasma glucose
Asemi et al[31], 2014a	Randomized, double-blind, placebo-controlled trial. Intervention arms: 2; Trial conducted in: Iran; Single centered trial; Trial duration: 6 wk; Obtained ethical clearance and participant consent. Funding information provided.Trial ID: IRCT201305115623N7	Participants diagnosed with GDM (used ADA criteria); 50 participants randomized into different treatment arms (vitamin D arm: n = 25, placebo arm: n = 25). Mean age of participants: -Vitamin D arm: 31.1 ± 5.5 yr; -Placebo arm: 30.8 ± 6.2 yr	Two intervention arms: (1) Vitamin D: 50,000 IU vitamin D3 pearl two times during the trial period (at baseline and day 21); and (2) Placebo	Attrition from vitamin D supplemented arm: n = 3; Other outcomes reported: (1) Newborn hyperbilirubinemia; (2) Newborn hospitalization; (3) Macrosomia; and (4) Cesarean section
Asemi et al[16], 2014b	Randomized, placebo-controlled clinical trial. Intervention arms: TwoMulti-centric trial. Trial duration: 6 wk. Trial conducted in: IranObtained ethical clearance and participant consent. Funding information provided. Clinical trial registration number: IRCT201311205623N11	Participants diagnosed with GDM (used ADA criteria); 56 participants randomized into different treatment arms (vitamin D and calcium: n = 28, placebo receiving group: n = 28). Mean age of participants: -Vitamin D and calcium receiving arm: 28.7 ± 6.0 yr; -Placebo receiving arm: 30.8 ± 6.6 yr	Two intervention arms: (1) 1000 mg calcium carbonate daily and 50000 U vitamin D3 at the baseline and day 21 of the study; and (2) Placebo	Attrition from vitamin D supplemented arm: n = 3. Other outcomes reported: Fasting plasma glucose
Karamali et al[32], 2016	Randomized, double-blind, placebo-controlled trial; Intervention arms: 2; Trial conducted in: Iran; Multicentric trialTrial duration: 6 wk; Obtained ethical clearance and participant consent. Funding information provided. Trial ID: IRCT201407115623N23	Participants diagnosed with GDM (used ADA criteria); 60 participants randomized into different treatment arms (vitamin D and calcium arm: n = 30; placebo arm: n = 30). Mean age of participants: -Vitamin D and calcium arm: 28·7 ± 6·1 yr; -Placebo arm: 31·6 ± 6·3 yr	Two intervention arms: (1) Vitamin D3 (50000 IU) at baseline and day 21 along with 1000 mg calcium carbonate daily; and (2) Placebo	No attrition from vitamin D supplemented arm; Other outcomes reported: (1) Newborn hyperbilirubinemia; (2) Newborn hospitalization; (3) Macrosomia; and (4) Cesarean section
Karamali et al[14], 2018	Randomized, double-blind, placebo-controlled trial; Intervention arms: 2; Single centered trial. Trial duration: 6 wk; Trial conducted in: Iran; Obtained ethical clearance (participant consent information unclear). Funding information provided. Trial registration details: Unclear	Participants diagnosed with GDM (used ADA criteria); 60 participants randomized into different treatment arms; (Magnesium, zinc, calcium and vitamin D supplements arm: n = 30; Placebo arm: n = 30); Mean age of participants: -Magnesium, zinc, calcium and vitamin D: 30.0 ± 4.5 yr; -Placebo arm: 31.1 ± 4.2 yr	Two intervention arms: (1) 100 mg magnesium, 4 mg zinc, 400 mg calcium and 200 IU vitamin D two times a day for 6 wk; and (2) Placebo	No attrition from vitamin D supplemented arm; Other outcomes reported: Fasting plasma glucose
Razavi et al[35], 2017	Randomized, double-blind, placebo-controlled, Intervention arms: 4; Trial conducted in: Iran. Single centered trial. Trial duration: 6 wk; Obtained ethical clearance and participant consent. Funding information provided. Trial ID: IRCT201701305623N106	Participants diagnosed with GDM (used ADA criteria); 120 participants randomized into different treatment arms (vitamin D and omega-3 arm: n = 30; omega-3 arm: n = 30; vitamin D arm: n = 30; placebo: n = 30); Mean age of participants: -Vitamin D and omega-3 arm: 29.9 ± 4.0 yr; -Omega-3 arm: 29.7 ± 3.6 yr; -Vitamin D arm: 29.9 ± 5.0 yr; -Placebo: 29.2 ± 3.4 yr	Four intervention arms: (1) Vitamin D (50000 IU): Two weekly two times a day; (2) Vitamin D (50000 IU) two weekly plus 1000 mg omega-3 fatty acids two times a day; (3) 1000 mg omega-3 fatty acids two times a day; and (4) Placebo	No attrition from vitamin D supplemented arm; Other outcomes reported: (1) Newborn hyperbilirubinemia; (2) Newborn hospitalization; (3) Macrosomia; and (4) Cesarean section
Valizadeh et al[34], 2016	Randomized controlled trial. Investigators and patients were not blinded. Intervention arms: 2; Single centered trial; Trial conducted in: Iran; Trial duration: Until delivery; Obtained ethical clearance and participant consent. Funding information provided. Trial ID: IRCT2012101611144N1	Participants diagnosed with GDM (used ADA criteria); 96 participants randomized into different treatment arms (vitamin D arm: n = 48; no supplement arm: n = 48); Mean age of participants: -Vitamin D arm: 32.0 ± 5.5 yr; -No supplement arm: 32.4 ± 4.7 yr	Two intervention arms: (1) 700000 IU vitamin D3 in total (regimen differed by gestational age of GDM patients); and (2) Comparison group did not receive any supplementation	Attrition from vitamin D supplemented arm: n = 4; Other outcomes reported: (1) Newborn hyperbilirubinemia; (2) Macrosomia; (3) Cesarean section; and (4) Fasting plasma glucose
Yazdchi et al[15], 2016	Randomized, double-blinded placebo-controlled clinical trial; Intervention arms: 2; Multi-center trial; Trial duration: 8 wk. Trial conducted in: Iran; Obtained ethical clearance and participant consent. Funding information provided. Clinical trial registration number: IRCT201306253140N11	Participants diagnosed with GDM (used International Association of Diabetes and Pregnancy Study Groups criteria); 76 participants randomized into different treatment arms: Vitamin D arm: n = 38; placebo arm: n = 38; Mean age of participants: -Vitamin D arm: 31.64 ± 4.40 yr; -Placebo arm: 32.11 ± 3.61 yr	Two intervention arms:(1) 50000 IU vitamin D3 oral capsules two weekly for 8 wk; and (2) Placebo	Attrition from vitamin D supplemented arm: n = 4; Other outcomes reported: Fasting plasma glucose
Zhang et al[38], 2016	Randomized, double-blind, placebo-controlled trial. Intervention arms: 4; Single centered trial. Trial duration: 24-28 wk of pregnancy to delivery; Trial conducted in: China; Obtained ethical clearance and participant consent. Funding information provided. Clinical trial registration details: Unclear	Participants diagnosed with GDM (criteria unclear). 133 participants randomized into different treatment arms (low dose vitamin D: n = 38; medium dose vitamin D: n = 38; high dose vitamin D: n = 37; placebo: n = 23); Mean age of participants: -Placebo arm: 29.8 ± 4.7; -Low dose vitamin D arm: 30.3 ± 5.1; -Medium dose vitamin D arm: 29.4 ± 4.9; -High dose vitamin D arm: 30.1 ± 4.5	Four intervention arms: (1) Low dose vitamin D: 200 IU daily; (2) Medium dose vitamin D: 2000 IU monthly; and (3) High dose vitamin D: 50000 IU every 2 wk. Placebo	Attrition from vitamin D supplemented arm: n = 4
Li and Xing[13], 2016	Randomized, double-blinded clinical trial. Intervention arms: 2. Multi-centric trial. Trial duration: 16 wk. Trial conducted in: China; Obtained ethical clearance and participant consent. Funding information provided. Clinical trial registration details: Unclear	Participants diagnosed with GDM (used ADA criteria)103 participants randomized into different treatment arms (yoghurt with vitamin D: n = 52, plain yoghurt: n = 51); Mean age of participants: -Yoghurt supplemented with vitamin D receiving arm: 29.0 ± 5.3 yr; -Plain yoghurt arm: 28.3 ± 4.1 yr	Two intervention arms: (1) Yoghurt was supplemented with 500 IU of vitamin D3 twice daily for 16 wk; and (2) plain yoghurt: Twice daily for 16 wk	Attrition from vitamin D supplemented arm: n = 4. Other outcomes reported: Fasting plasma glucose

ADA: American diabetes association.