Comparison 1. Supplementation with vitamin D alone versus placebo or no intervention (no vitamins or minerals).

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Pre‐eclampsia (ALL)	4	499	Risk Ratio (M‐H, Random, 95% CI)	0.48 [0.30, 0.79]
2 Gestational diabetes (ALL)	4	446	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.27, 0.97]
3 Maternal adverse events	2		Risk Ratio (M‐H, Random, 95% CI)	Subtotals only
3.1 Severe postpartum haemorrhage	1	1134	Risk Ratio (M‐H, Random, 95% CI)	0.68 [0.51, 0.91]
3.2 Nephritic syndrome	1	135	Risk Ratio (M‐H, Random, 95% CI)	0.17 [0.01, 4.06]
3.3 Hypercalcaemia	1	1134	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
4 Preterm birth (less than 37 weeks' gestation) (ALL)	7	1640	Risk Ratio (M‐H, Random, 95% CI)	0.66 [0.34, 1.30]
5 Low birthweight (less than 2500 g) (ALL)	5	697	Risk Ratio (M‐H, Random, 95% CI)	0.55 [0.35, 0.87]
6 Pre‐eclampsia (by start of supplementation)	4	499	Risk Ratio (M‐H, Random, 95% CI)	0.48 [0.30, 0.79]
6.1 Less than 20 weeks of pregnancy	1	138	Risk Ratio (M‐H, Random, 95% CI)	0.29 [0.06, 1.37]
6.2 20 weeks of pregnancy or more	2	219	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.21, 1.24]
6.3 Unknown/unreported/mixed	1	142	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.27, 0.98]
7 Pre‐eclampsia (by pre‐gestational BMI)	4	499	Risk Ratio (M‐H, Random, 95% CI)	0.48 [0.30, 0.79]
7.1 Underweight (lower than 18.5)	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
7.2 Normal weight (18.5 to 24.9)	1	165	Risk Ratio (M‐H, Random, 95% CI)	0.53 [0.21, 1.33]
7.3 Overweight (25 or higher)	1	54	Risk Ratio (M‐H, Random, 95% CI)	0.33 [0.01, 7.84]
7.4 Unknown/unreported/mixed	2	280	Risk Ratio (M‐H, Random, 95% CI)	0.47 [0.26, 0.86]
8 Pre‐eclampsia (by supplementation scheme/regimen)	4	499	Risk Ratio (M‐H, Random, 95% CI)	0.48 [0.30, 0.79]
8.1 Single dose	1	165	Risk Ratio (M‐H, Random, 95% CI)	0.53 [0.21, 1.33]
8.2 Daily	2	192	Risk Ratio (M‐H, Random, 95% CI)	0.30 [0.08, 1.20]
8.3 Weekly/monthly	1	142	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.27, 0.98]
9 Pre‐eclampsia (by skin pigmentation based on Fitzpatrick skin tone chart)	4	499	Risk Ratio (M‐H, Random, 95% CI)	0.48 [0.30, 0.79]
9.1 Three or less	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
9.2 Four or more	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
9.3 Unknown/unreported/mixed	4	499	Risk Ratio (M‐H, Random, 95% CI)	0.48 [0.30, 0.79]
10 Pre‐eclampsia (by latitude)	4	499	Risk Ratio (M‐H, Random, 95% CI)	0.48 [0.30, 0.79]
10.1 Between Tropics of Cancer and Capricorn	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
10.2 North of the Tropic of Cancer or South of the Tropic of Capricorn	4	499	Risk Ratio (M‐H, Random, 95% CI)	0.48 [0.30, 0.79]
10.3 Unknown/unreported	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
11 Pre‐eclampsia (by season at the start of pregnancy)	4	499	Risk Ratio (M‐H, Random, 95% CI)	0.48 [0.30, 0.79]
11.1 Summer	1	54	Risk Ratio (M‐H, Random, 95% CI)	0.33 [0.01, 7.84]
11.2 Fall	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
11.3 Winter	1	138	Risk Ratio (M‐H, Random, 95% CI)	0.29 [0.06, 1.37]
11.4 Mixed/unknown	2	307	Risk Ratio (M‐H, Random, 95% CI)	0.52 [0.31, 0.88]
12 Gestational diabetes (by start of supplementation)	4	446	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.27, 0.97]
12.1 Less than 20 weeks of pregnancy	1	140	Risk Ratio (M‐H, Random, 95% CI)	0.88 [0.34, 2.28]
12.2 20 weeks of pregnancy or more	2	219	Risk Ratio (M‐H, Random, 95% CI)	0.43 [0.05, 3.45]
12.3 Unknown/unreported/mixed	1	87	Risk Ratio (M‐H, Random, 95% CI)	0.33 [0.13, 0.82]
13 Gestational diabetes (by pre‐gestational BMI)	4	446	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.27, 0.97]
13.1 Underweight (lower than 18.5)	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
13.2 Normal weight (18.5 to 24.9)	2	305	Risk Ratio (M‐H, Random, 95% CI)	0.83 [0.33, 2.05]
13.3 Overweight (25 or higher)	2	141	Risk Ratio (M‐H, Random, 95% CI)	0.33 [0.13, 0.79]
13.4 Unknown/unreported/mixed	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
14 Gestational diabetes (by supplementation scheme/regimen)	4	446	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.27, 0.97]
14.1 Single dose	1	165	Risk Ratio (M‐H, Random, 95% CI)	0.53 [0.03, 8.28]
14.2 Daily	2	141	Risk Ratio (M‐H, Random, 95% CI)	0.33 [0.13, 0.79]
14.3 Weekly/monthly	1	140	Risk Ratio (M‐H, Random, 95% CI)	0.88 [0.34, 2.28]
15 Gestational diabetes (by skin pigmentation based on Fitzpatrick skin tone chart)	4	446	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.27, 0.97]
15.1 Three or less	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
15.2 Four or more	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
15.3 Unknown/unreported/mixed	4	446	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.27, 0.97]
16 Gestational diabetes (by latitude)	4	446	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.27, 0.97]
16.1 Between Tropics of Cancer and Capricorn	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
16.2 North of the Tropic of Cancer or South of the Tropic of Capricorn	4	446	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.27, 0.97]
16.3 Unknown/unreported	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
17 Gestational diabetes (by season at the start of supplementation)	4	446	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.27, 0.97]
17.1 Summer	1	54	Risk Ratio (M‐H, Random, 95% CI)	0.33 [0.01, 7.84]
17.2 Fall	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
17.3 Winter	1	140	Risk Ratio (M‐H, Random, 95% CI)	0.88 [0.34, 2.28]
17.4 Mixed/unknown	2	252	Risk Ratio (M‐H, Random, 95% CI)	0.34 [0.14, 0.82]
18 Preterm birth (less than 37 weeks' gestation) (by start of supplementation)	7	1640	Risk Ratio (M‐H, Random, 95% CI)	0.66 [0.34, 1.30]
18.1 Less than 20 weeks of pregnancy	3	1149	Risk Ratio (M‐H, Random, 95% CI)	0.73 [0.26, 2.04]
18.2 20 weeks of pregnancy or more	4	491	Risk Ratio (M‐H, Random, 95% CI)	0.49 [0.13, 1.87]
18.3 Unknown/unreported/mixed	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
19 Preterm birth (less than 37 weeks' gestation) (by pre‐gestational BMI)	7	1640	Risk Ratio (M‐H, Random, 95% CI)	0.66 [0.34, 1.30]
19.1 Underweight (lower than 18.5)	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
19.2 Normal weight (18.5 to 24.9)	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
19.3 Overweight (25 or higher)	2	138	Risk Ratio (M‐H, Random, 95% CI)	0.60 [0.15, 2.46]
19.4 Unknown/unreported/mixed	5	1502	Risk Ratio (M‐H, Random, 95% CI)	0.64 [0.27, 1.54]
20 Preterm birth (less than 37 weeks' gestation) (by supplementation scheme/regimen)	7	1640	Risk Ratio (M‐H, Random, 95% CI)	0.66 [0.34, 1.30]
20.1 Single dose	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
20.2 Daily	6	1495	Risk Ratio (M‐H, Random, 95% CI)	0.61 [0.23, 1.58]
20.3 Weekly/monthly	1	145	Risk Ratio (M‐H, Random, 95% CI)	0.70 [0.32, 1.54]
21 Preterm birth (less than 37 weeks' gestation) (by skin pigmentation based on Fitzpatrick skin tone chart)	9	1943	Risk Ratio (M‐H, Random, 95% CI)	0.52 [0.30, 0.91]
21.1 Three or less	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
21.2 Four or more	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
21.3 Unknown/unreported/mixed	9	1943	Risk Ratio (M‐H, Random, 95% CI)	0.52 [0.30, 0.91]
22 Preterm birth (less than 37 weeks' gestation) (by latitude)	7	1640	Risk Ratio (M‐H, Random, 95% CI)	0.66 [0.34, 1.30]
22.1 Between Tropics of Cancer and Capricorn	2	358	Risk Ratio (M‐H, Random, 95% CI)	0.25 [0.05, 1.34]
22.2 North of the Tropic of Cancer or South of the Tropic of Capricorn	5	1282	Risk Ratio (M‐H, Random, 95% CI)	0.99 [0.59, 1.66]
22.3 Unknown/unreported	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
23 Preterm birth (less than 37 weeks' gestation) (by season at the start of supplementation)	7	1640	Risk Ratio (M‐H, Random, 95% CI)	0.66 [0.34, 1.30]
23.1 Summer	2	199	Risk Ratio (M‐H, Random, 95% CI)	0.72 [0.34, 1.53]
23.2 Winter	1	34	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
23.3 Mixed/unknown	4	1407	Risk Ratio (M‐H, Random, 95% CI)	0.55 [0.19, 1.66]
24 Low birthweight (less than 2500 g) (by start of supplementation)	3	491	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.24, 0.65]
24.1 Less than 20 weeks of pregnancy	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
24.2 20 weeks of pregnancy or more	3	491	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.24, 0.65]
24.3 Unknown/unreported/mixed	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
25 Low birthweight (less than 2500 g) (by pre‐gestational BMI)	3	491	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.24, 0.65]
25.1 Underweight (lower than 18.5)	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
25.2 Normal weight (18.5 to 24.9)	1	165	Risk Ratio (M‐H, Random, 95% CI)	0.43 [0.19, 0.98]
25.3 Overweight (25 or higher)	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
25.4 Unknown/unreported/mixed	2	326	Risk Ratio (M‐H, Random, 95% CI)	0.35 [0.14, 0.88]
26 Low birthweight (less than 2500 g) (by supplementation scheme/regimen)	3	491	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.24, 0.65]
26.1 Single dose	2	365	Risk Ratio (M‐H, Random, 95% CI)	0.32 [0.16, 0.65]
26.2 Daily	1	126	Risk Ratio (M‐H, Random, 95% CI)	0.53 [0.23, 1.21]
26.3 Weekly/monthly	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
27 Low birthweight (less than 2500 g) (by skin pigmentation based on Fitzpatrick skin to	3	491	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.24, 0.65]
27.1 Three or less	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
27.2 Four or more	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
27.3 Unknown/unreported/mixed	3	491	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.24, 0.65]
28 Low birthweight (less than 2500 g) (by latitude)	3	491	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.24, 0.65]
28.1 Between Tropics of Cancer and Capricorn	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
28.2 North of the Tropic of Cancer or South of the Tropic of Capricorn	3	491	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.24, 0.65]
28.3 Unknown/unreported	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
29 Low birthweight (less than 2500 g) (by season at the start of pregnancy)	3	491	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.24, 0.65]
29.1 Summer	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
29.2 Fall	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
29.3 Winter	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
29.4 Mixed/unknown	3	491	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.24, 0.65]
30 Caesarean section	10	1104	Risk Ratio (M‐H, Random, 95% CI)	0.98 [0.80, 1.21]
31 Gestational hypertension	2	1130	Risk Ratio (M‐H, Random, 95% CI)	0.78 [0.41, 1.49]
32 Maternal death (death while pregnant or within 42 days of termination of pregnancy) (ALL)	1	180	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
33 Maternal vitamin D concentration at term (25‐hydroxyvitamin D) (nmol/L) (ALL)	14	2470	Mean Difference (IV, Random, 95% CI)	35.66 [24.19, 47.13]
34 Birth length (cm)	8	931	Mean Difference (IV, Random, 95% CI)	0.57 [0.19, 0.95]
35 Head circumference at birth (cm)	8	1841	Mean Difference (IV, Random, 95% CI)	0.11 [‐0.21, 0.44]
36 Birthweight (g)	17	2828	Mean Difference (IV, Random, 95% CI)	80.30 [‐14.40, 175.00]
37 Stillbirth	3	584	Risk Ratio (M‐H, Random, 95% CI)	0.35 [0.06, 1.98]
38 Neonatal death	2	326	Risk Ratio (M‐H, Random, 95% CI)	0.27 [0.04, 1.67]
39 Apgar score less than seven at five minutes	1	165	Risk Ratio (M‐H, Random, 95% CI)	0.53 [0.11, 2.53]