Comparison 1. Metformin versus placebo.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Large‐for‐gestational‐age infant, defined as birthweight ≥ 90th percentile for gestational age and infant sex	2	831	Risk Ratio (M‐H, Fixed, 95% CI)	0.95 [0.70, 1.30]
2 Gestational weight gain (kg)	3	899	Mean Difference (IV, Random, 95% CI)	‐2.60 [‐5.29, 0.10]
3 Gestational hypertension	3	1040	Risk Ratio (M‐H, Random, 95% CI)	1.02 [0.54, 1.94]
4 Pre‐eclampsia	2	840	Risk Ratio (M‐H, Random, 95% CI)	0.74 [0.09, 6.28]
5 Gestational diabetes	3	892	Risk Ratio (M‐H, Fixed, 95% CI)	0.85 [0.61, 1.19]
6 Preterm birth (before 37 weeks)	2	831	Risk Ratio (M‐H, Random, 95% CI)	0.89 [0.41, 1.93]
7 Preterm premature rupture of membranes	1	400	Risk Ratio (M‐H, Fixed, 95% CI)	0.65 [0.19, 2.28]
8 Induction of labour	1	435	Risk Ratio (M‐H, Fixed, 95% CI)	0.84 [0.67, 1.06]
9 Vaginal birth	2	832	Risk Ratio (M‐H, Fixed, 95% CI)	1.06 [0.95, 1.18]
10 Caesarean birth	2	838	Risk Ratio (M‐H, Fixed, 95% CI)	0.91 [0.76, 1.08]
11 Shoulder dystocia	2	846	Risk Ratio (M‐H, Fixed, 95% CI)	0.54 [0.12, 2.53]
12 Third‐ or fourth‐degree perineal tear	1	397	Risk Ratio (M‐H, Fixed, 95% CI)	1.93 [0.18, 21.12]
13 Adverse effects of the treatment: at least one	1	400	Risk Ratio (M‐H, Fixed, 95% CI)	1.63 [1.27, 2.08]
14 Adverse effects of the treatment: abdominal pain	2	797	Risk Ratio (M‐H, Fixed, 95% CI)	1.12 [0.81, 1.54]
15 Adverse effects of the treatment: diarrhoea	2	797	Risk Ratio (M‐H, Fixed, 95% CI)	2.34 [1.74, 3.14]
16 Adverse effects of the treatment: headache	2	797	Risk Ratio (M‐H, Random, 95% CI)	1.32 [0.64, 2.70]
17 Postpartum haemorrhage	2	825	Risk Ratio (M‐H, Fixed, 95% CI)	1.05 [0.68, 1.61]
18 Birthweight (g)	2	834	Mean Difference (IV, Fixed, 95% CI)	6.39 [‐81.15, 93.92]
19 Hypoglycaemia requiring treatment	1	397	Risk Ratio (M‐H, Fixed, 95% CI)	0.79 [0.33, 1.86]
20 Hyperbilirubinaemia requiring treatment	1	397	Risk Ratio (M‐H, Fixed, 95% CI)	0.71 [0.33, 1.50]
21 Birth trauma	1	397	Risk Ratio (M‐H, Fixed, 95% CI)	0.97 [0.20, 4.73]
22 Apgar less than 7 at five minutes	1	397	Risk Ratio (M‐H, Fixed, 95% CI)	0.32 [0.03, 3.07]
23 NICU/Neonatal unit admission	1	397	Risk Ratio (M‐H, Fixed, 95% CI)	0.76 [0.35, 1.63]
24 Stillbirth	2	843	Risk Ratio (M‐H, Fixed, 95% CI)	1.39 [0.28, 6.97]
25 Neonatal death	2	834	Risk Ratio (M‐H, Fixed, 95% CI)	0.43 [0.06, 2.91]