Methods	Randomized, placebo-controlled trial; 4 parallel groups (3 treatment, 1 placebo)
	Unit of randomization: individual.
Participants	Dates of data collection: October 1986 to February 1987.
	Setting: Prince ofWales Hospital, Hong Kong; mostly suburban or rural Chinese women of lower or middle class
	Inclusion criteria: all women undergoing CS.
	Exclusion criteria: receiving antibiotics; pyrexia >37.4°C; diagnosed infection; increased risk of infection, e.g. diabetes; known sensitivity to the antibiotics
Interventions	IV at time of induction of anesthesia: ampicillin 1 g (N = 96); ampicillin 1 g and metronidazole 500 mg (N = 104); ampicillin 1 g and sulbactam 500 mg (N = 99), vs placebo (normal saline) (N = 101). Results of the 3 treatment groups combined
Outcomes	Febrile morbidity (oral temperature of more than 38°C at least twice after day 1); wound infection (induration, serosanguinous discharge or dehiscence with purulent discharge) ; UTI (positive culture); genital tract infection (pain and uterine tenderness, purulent uterine discharge with microbiological confirmation); any infection anywhere (antibiotic 75/299 vs placebo 28/101); post-operative antibiotic use (22/299 vs 9/101)
Notes	Only moderate or prolonged febrile morbidity (as defined) included
	Class of antibiotic: Aminopenicillin (ampicillin), nitroimidazole (metronidazole), beta-lactam/beta-lactamase inhibitor
	Subgroups:
	type of CS unclear; before cord clamping.
Risk of bias
Item	Authors’ judgement	Description
Adequate sequence generation?	Unclear	“list of random numbers consulted by nurse.”
		No additional information.
Allocation concealment?	Unclear	“list of random numbers consulted by nurse.”
Blinding?	Yes	Double blind’ randomized trial (the anesthetist was not blind)
All outcomes
		Placebo (normal saline).
		“All doctors and nurses looking after the patients were ignorant of the drug given until the end of the study.”
Incomplete outcome data addressed?	Yes	No loss to follow up
All outcomes		No participants excluded
		ITT analysis
Free of selective reporting?	Unclear	Insufficient information to judge
Free of other bias?	Unclear	The groups were comparable regarding age, parity, primary CS, indication for CS, urinary catheterization and vaginal examination before operation. There was insufficient other information which to judge
Overall low risk of bias?	Unclear	Sequence generation and concealment allocation are unclear.