Comparison 1. (1.1) Nitric oxide donors versus placebo/no intervention (all women).

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Vaginal delivery not achieved in 24 hours	1	238	Risk Ratio (M‐H, Fixed, 95% CI)	0.97 [0.83, 1.15]
2 Uterine hyperstimulation with FHR changes	2	300	Risk Ratio (M‐H, Fixed, 95% CI)	0.09 [0.01, 1.62]
3 Caesarean section	9	2624	Risk Ratio (M‐H, Fixed, 95% CI)	0.99 [0.88, 1.11]
4 Serious neonatal morbidity/perinatal death	2	1712	Risk Ratio (M‐H, Random, 95% CI)	1.61 [0.08, 33.26]
5 Serious maternal morbidity or death	1	1362	Risk Ratio (M‐H, Fixed, 95% CI)	0.0 [0.0, 0.0]
6 Cervix unfavourable/unchanged after 12‐24 hours	4	762	Risk Ratio (M‐H, Random, 95% CI)	0.78 [0.67, 0.90]
6.1 Standard release	4	659	Risk Ratio (M‐H, Random, 95% CI)	0.81 [0.69, 0.94]
6.2 Slow release	1	103	Risk Ratio (M‐H, Random, 95% CI)	0.63 [0.49, 0.82]
7 Oxytocin augmentation	4	1916	Risk Ratio (M‐H, Random, 95% CI)	0.95 [0.84, 1.07]
8 Uterine hyperstimulation without FHR changes	1	200	Risk Ratio (M‐H, Fixed, 95% CI)	0.05 [0.00, 0.80]
9 Epidural analgesia	1	350	Risk Ratio (M‐H, Fixed, 95% CI)	0.94 [0.82, 1.09]
10 Instrumental vaginal delivery	4	1835	Risk Ratio (M‐H, Fixed, 95% CI)	0.96 [0.83, 1.10]
11 Meconium‐stained liquor	3	699	Risk Ratio (M‐H, Fixed, 95% CI)	0.89 [0.69, 1.14]
12 Apgar score < 7 at 5 minutes	5	2212	Risk Ratio (M‐H, Fixed, 95% CI)	1.06 [0.54, 2.07]
13 Neonatal intensive care unit admission	5	873	Risk Ratio (M‐H, Random, 95% CI)	0.83 [0.47, 1.46]
14 Perinatal death	2	1712	Risk Ratio (M‐H, Fixed, 95% CI)	0.33 [0.01, 7.94]
15 Maternal side effects (all)	1	1362	Risk Ratio (M‐H, Fixed, 95% CI)	2.82 [2.49, 3.20]
16 Maternal side effects (nausea)	3	1782	Risk Ratio (M‐H, Random, 95% CI)	2.44 [1.47, 4.05]
17 Maternal side effects (headache)	6	2085	Risk Ratio (M‐H, Random, 95% CI)	6.59 [3.97, 10.95]
18 Maternal side effects (vomiting)	1	1362	Risk Ratio (M‐H, Fixed, 95% CI)	2.42 [1.54, 3.81]
19 Maternal side effects (diarrhoea)	1	1362	Risk Ratio (M‐H, Fixed, 95% CI)	1.44 [0.95, 2.19]
20 Postpartum haemorrhage	2	1562	Risk Ratio (M‐H, Fixed, 95% CI)	1.12 [0.90, 1.40]
21 Women not satisfied	1	1362	Risk Ratio (M‐H, Fixed, 95% CI)	1.06 [0.82, 1.38]
22 Additional induction agents used	5	2180	Risk Ratio (M‐H, Random, 95% CI)	0.71 [0.58, 0.88]
22.1 Standard release	5	2077	Risk Ratio (M‐H, Random, 95% CI)	0.73 [0.58, 0.92]
22.2 Slow release	1	103	Risk Ratio (M‐H, Random, 95% CI)	0.63 [0.49, 0.82]