Abstract: We included 13 studies, involving 1622 women. All were comparisons of single-dose treatment with short-course (four- to seven-day) treatments. The risk of bias of trials included in this review was largely unclear, and most trials were at high risk of performance bias. The quality of the evidence was assessed using the GRADE approach. When the any antibiotic agent was used, the 'no cure' rate for asymptomatic bacteriuria in pregnant women was slightly lower for the short-course treatment over the single-dose treatment, although there was evidence of statistical heterogeneity (average risk ratio (RR) 1.28, 95% confidence interval (CI) 0.87 to 1.88; women = 1502, studies = 13; I² = 56%; very low quality evidence). Data from only good quality trials also showed better cure rates with short (four- to seven-day) regimens of the same microbial agent (average RR 1.72, 95% CI 1.27 to 2.33; women = 803, studies = two; I² = 0%; high quality evidence). There was no clear difference in the recurrence of asymptomatic bacteriuria rate between treatment and control groups, whether the same or different microbial agents were used (RR 1.13, 95% CI 0.77 to 1.66; 445 women studies = eight; I² = 0%; very low quality evidence). Differences were detected for low birthweight babies, favoring a short course (four- to seven-day treatment) of the same microbial agent, although the data come from a single trial (RR 1.65, 95% CI 1.06 to 2.57; 714 women; high quality evidence), but no differences were observed for preterm delivery (RR 1.17, 95% CI 0.77 to 1.78; women = 804; studies = three; I² = 23%; moderate quality) or pyelonephritis (RR 3.09, 95% CI 0.54 to 17.55; women = 102; studies = two; I² = 0%; very low quality evidence). Finally, single-dose treatment of any microbial agent was associated with a decrease in reports of 'any side effects' (RR 0.70, 95% CI 0.56 to 0.88; 1460 women, studies = 12; I² = 9%; low quality evidence). Evidence was downgraded for risk of bias concerns in trials contributing data and for imprecise effect estimates (wide confidence intervals crossing the line of no effect, and in some cases, small studies with few events). A single-dose regimen of antibiotics may be less effective than a short-course (four- to seven-day) regimen, but more evidence is needed from large trials measuring important outcomes, such as cure rate. Women with asymptomatic bacteriuria in pregnancy should be treated by the standard regimen of antibiotics until more data become available testing seven-day treatment compared with shorter courses of three- or five-day regimens.

Plain-language summary: This review aimed to identify whether single-dose antibiotic treatments are as effective as longer ones for maternal and newborn outcomes. In general, the risk of bias of trials included in this review was largely unclear. The overall quality of the evidence was assessed using the GRADE approach. The review of 13 studies, involving over 1622 women, found that a seven-day regimen is more effective than a one-day course, especially for the outcome of low birthweight (high quality evidence), but this result is based on just one study. There were no clear differences between a single dose and a four- to seven-day short course of antibiotics for other review outcomes, including kidney infection (very low quality evidence) and preterm birth (moderate quality evidence). Women with a single-dose regimen reported fewer side effects (low quality evidence). More trials are needed to confirm which length of treatment is best for women and babies.