Association between asymptomatic bacteriuria in pregnancy and adverse pregnancy- and births outcomes. A systematic review

Existing guidelines for screening and treatment of asymptomatic bacteriuria (ASB) in pregnancy are based on studies completed more than 30 years ago. This evidence is characterized by a lack of consensus on the association between ASB and adverse pregnancy- and birth outcomes.

This systematic review aimed to investigate the association between untreated/treated ASB (≥10⁵ colony-forming units (cfu) of the same bacteria per ml urine in two consecutive voided cultures without any symptoms) and pregnancy outcomes (pyelonephritis, chorioamnionitis, prelabour rupture of membranes (PROM)), and birth outcomes (preterm birth (PTB), low birth weight (LBW) and small for gestational age (SGA)). The impact of the most serious pathogens E. coli and Group B streptococci (GBS) on these outcomes was also examined.

A systematic literature search was prepared according to the guideline Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA). The search was conducted in the databases Medline, Embase, and Cochrane Library, with a systematic strategy based on the PICO acronym (Population, Intervention, Comparison, Outcome). Covidence was used as a screening- and data extraction tool. Randomized trials and observational studies published between, January 01, 2005-February 10, 2023, were identified. The Cochrane Collaboration risk of bias tool 2 and the Newcastle-Ottawa Quality Assessment Scale were applied to assess the quality of the included studies. A protocol was published prior to this review, at the international prospective register of systematic reviews (PROSPERO).

The database search yielded 3029 records. Fourteen studies were included. Untreated pregnant women with ASB had significantly increased odds of pyelonephritis. Most of the studies showed no significant association between treated ASB and pyelonephritis. In treated ASB, an increased risk of both chorioamnionitis and PROM was found. Divergent results were found in the association between ASB and PTB, as well as in the association between untreated ASB and LBW. Most of the studies showed no significant association between treated ASB and LBW. One study found no significant association between untreated/treated ASB and SGA. No studies were identified that addressed the association between ASB with E. coli/GBS and the outcomes examined.

There is a need for more recent high-quality studies to investigate the association between untreated/treated ASB and pregnancy- and birth outcomes, and to assess the impact of E. coli/GBS on these outcomes.