Ruiz‐Moreno 1991.

Methods	Randomized, placebo‐controlled; 2 parallel groups. Unit of randomization: individual.
Participants	Dates of data collection: not reported. Setting:Hospital Central Militar, Mexico city, Mexico. Women predominantly (78%) of low socioeconomic level. Inclusion criteria: women in active labor undergoing CS. N = 100. Exclusion: elective CS, evidence of infection, antibiotic use within 8 days, metronidazole intolerance, lack of consent.
Interventions	Intervention: nitroimidazole: metronidazole 1 g IV; N = 50. Comparison: placebo: identical appearing placebo; N = 50. Immediately after cord clamping.
Outcomes	Endometritis (purulent and/or foul odor lochia); wound infection (wound edges tender, red and swollen, or frank pus or sanguino‐purulent material exuded); UTI (bacteria seen in sediment); maternal hospital stay.
Notes	Class of antibiotic: nitroimidazole (metronidazole). Subgroups: non‐elective CS; after cord clamping. The 2 groups reported as comparable regarding age and parity, etc.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "...randomized..". Comment: no description of sequence generation process.
Allocation concealment (selection bias)	Unclear risk	Comment: no information provided.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Comment: no losses or exclusions were reported. Appears to be ITT analysis.
Selective reporting (reporting bias)	Unclear risk	Comment: insufficient information to judge.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Comment: double‐blind; identical appearing placebo.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: insufficient information to judge.
Other bias	Low risk	Comment: no other sources of bias identified.