Background
Antibiotics for bacteriuria and urinary tract infection are commonly prescribed during pregnancy to avoid adverse pregnancy outcomes. The aim of this study was to evaluate the association between significant bacteriuria in pregnancy and any of the four pregnancy outcomes: preterm delivery; low birth weight; small for gestational age; and preterm labour.

Methods
Systematic review with meta-analysis of observational studies. We searched PubMed, EMBASE, the Cochrane CENTRAL library, and Web of Science for observational studies published before 1 March 2022. The risk of bias was assessed using the Newcastle–Ottawa scale. Study identification, data extraction and risk-of-bias assessment was performed by two independent authors. We combined the included studies in meta-analyses and expressed results as ORs with 95% CIs (Prospero CRD42016053485).

Results
We identified 58 studies involving 421 657 women. The quality of the studies was mainly poor or fair. The pooled, unadjusted OR for the association between any significant bacteriuria and: (i) preterm delivery was 1.62 (95% CI: 1.30–2.01; 27 studies; I2 = 61%); (ii) low birth weight was 1.50 (95% CI: 1.30–1.72; 47 studies; I2 = 74%); (iii) preterm labour was 2.29 (95% CI: 1.53–3.43; 3 studies; I2 = 0%); and (iv) small for gestational age was 1.33 (95% CI: 0.88–2.02; 7 studies; I2 = 54%). Four studies provided an adjusted OR, but were too diverse to combine in meta-analysis.

Conclusions
This systematic review identified an association between significant bacteriuria in pregnancy and the three complications: preterm delivery; low birth weight; and preterm labour. However, the quality of the available evidence is insufficient to conclude whether this association is merely due to confounding factors. There is a lack of high-quality evidence to support active identification and treatment of bacteriuria in pregnancy.