Summary of findings for the main comparison. Antibiotics compared to no treatment for asymptomatic bacteriuria in pregnancy.

Antibiotics compared to no treatment for asymptomatic bacteriuria in pregnancy
Patient or population: pregnant women with asymptomatic bacteriuria Setting: hospital‐based clinics in North America, UK and Ireland, Australia; hospital and community midwifery practices in the Netherlands Intervention: antibiotics Comparison: no treatment
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with no treatment	Risk with antibiotics
Development of pyelonephritis	Study population		RR 0.24 (0.13 to 0.41)	2017 (12 RCTs)	⊕⊕⊝⊝ Lowa,b
	199 per 1000	48 per 1000 (26 to 82)
Preterm birth < 37 weeks	Study population		RR 0.34 (0.13 to 0.88)	327 (3 RCTs)	⊕⊕⊝⊝ Lowc,d
	174 per 1000	59 per 1000 (23 to 153)
Birthweight < 2500 g	Study population		RR 0.64 (0.45 to 0.93)	1437 (6 RCTs)	⊕⊕⊝⊝ Lowe,f
	136 per 1000	87 per 1000 (61 to 126)
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; RR: Risk ratio; OR: Odds ratio;
GRADE Working Group grades of evidence High certainty: We are very confident that the true effect lies close to that of the estimate of the effect Moderate certainty: We are moderately confident in the effect estimate: The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different Low certainty: Our confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect Very low certainty: We have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of effect

^aWe downgraded 1 level for serious limitations in study design: most of the trials contributing outcome data either had important design limitations related to lack of allocation concealment and lack of blinding, or there were insufficient details provided in the report to assess risk of bias. Many of the studies were performed in the 1960s and 1970s, prior to more rigorous study designs and reporting standards.
 ^bWe downgraded 1 level for serious limitations in inconsistency: the rate of pyelonephritis in the control groups ranged from 2.2% to 36%; there was significant heterogeneity, which was not explained by the duration of treatment (I² = 60%).
 ^cWe downgraded 1 level for serious limitations in study design: only one trial was judged at low risk of bias across all domains; for the other two, the risk of bias was either unclear because details were not provided, or judged high risk.
 ^dWe downgraded 1 level for serious limitations in indirectness: the rate of preterm birth in the control group ranged from 4.4% to 37.5%. There have been substantial changes in obstetric practices over the four decades from the earliest to the latest study. In one study, only women with group B streptococcus bacteriuria were enrolled, and treatment was with penicillin.
 ^eWe downgraded 1 level for serious limitations in study design: all of the trials contributing outcome data either had important design limitations related to lack of allocation concealment and lack of blinding, or there were insufficient details provided in the report to assess risk of bias. The studies contributing data to this outcome were performed in the 1960s and 1970s, prior to more rigorous study designs and reporting standards.
 ^fWe downgraded 1 level for serious limitations in indirectness: 5 of the 6 studies included in this outcome continued antibiotic treatment for 6 weeks (1 study), or until term (4 studies). In one study, women received a single dose of antibiotics, and in no study did women receive what is now considered a standard course of antibiotics for 3 to 7 days.