Comparison 6. (1.6) Nitric oxide donors versus placebo/no intervention (all primiparae, intact membranes, unfavourable cervix).

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 Caesarean section	1	354	Risk Ratio (M‐H, Fixed, 95% CI)	1.16 [0.87, 1.55]
3 Serious neonatal morbidity/perinatal death	1	350	Risk Ratio (M‐H, Fixed, 95% CI)	0.33 [0.01, 7.94]
4 Cervix unfavourable/unchanged after 12‐24 hours	1	257	Risk Ratio (M‐H, Fixed, 95% CI)	0.78 [0.42, 1.44]
5 Oxytocin augmentation	1	254	Risk Ratio (M‐H, Fixed, 95% CI)	1.07 [0.88, 1.30]
6 Epidural analgesia	1	350	Risk Ratio (M‐H, Fixed, 95% CI)	0.94 [0.82, 1.09]
7 Instrumental vaginal delivery	1	350	Risk Ratio (M‐H, Fixed, 95% CI)	0.85 [0.61, 1.18]
8 Meconium‐stained liquor	1	350	Risk Ratio (M‐H, Fixed, 95% CI)	0.94 [0.68, 1.30]
9 Apgar score < 7 at 5 minutes	1	350	Risk Ratio (M‐H, Fixed, 95% CI)	1.47 [0.25, 8.67]
10 Neonatal intensive care unit admission	1	350	Risk Ratio (M‐H, Fixed, 95% CI)	1.10 [0.58, 2.09]
11 Perinatal death	1	350	Risk Ratio (M‐H, Fixed, 95% CI)	0.33 [0.01, 7.94]
12 Maternal side effects (nausea)	1	220	Risk Ratio (M‐H, Fixed, 95% CI)	1.41 [0.73, 2.71]
13 Maternal side effects (headache)	1	220	Risk Ratio (M‐H, Fixed, 95% CI)	3.24 [2.18, 4.82]
14 Additional induction agents used	1	257	Risk Ratio (M‐H, Fixed, 95% CI)	0.83 [0.70, 0.97]