Asymptomatic bacteriuria in pregnancy - Is it still necessary to screen & treat?

Abstract

Asymptomatic bacteriuria (ASB) in pregnancy occurs in 2–10% of pregnant women although higher frequencies have also been reported, up to 40%. Pregnant women are more prone to develop urinary tract infections (UTI) because of dilatation of the renal system and decreased peristalsis of the ureters and bladder facilitating bacterial colonisation and ascending infection in pregnancy. Enterobacteriaceae comprise approximately the majority of urine isolates, of which Escherichia coli is the most common pathogen. A urine culture is considered the gold standard for diagnosing bacteriuria. The biggest challenge however is differentiating between significant (disease) and insignificant colonisation (not related to symptoms or adverse events) of the urinary tract. In addition, it is not clear which microorganisms are considered uropathogens and which are contaminants resulting in a wide range of reported incidences of ASB. ASB when considered a latent stage and UTI as a symptomatic stage are both recognizable conditions that may be associated with an increased risk of adverse pregnancy outcomes. However, most pregnant women who developed a symptomatic UTI did not suffer from bacteriuria at the moment of screening (often performed in the first half of pregnancy) and not all women with ASB develop a UTI. In addition, the optimal timing of ASB screening remains unclear because ASB is often not a permanent stage and can dissolve spontaneously. It has always been suggested that untreated ASB is an important risk factor for preterm birth, however when critically reviewing the literature, we found that currently there is no clear causal association between untreated ASB in pregnant women and preterm birth. Recent studies showed that the incidence of antepartum pyelonephritis has decreased in developed countries with estimated incidences between 0.07% and 0.5%. This decrease is also notable in countries without a screen and treat program for ASB thereby questioning the effectiveness of current screening programs. There is much debate about the best pharmacological and/or non-pharmacological treatment for ASB. There is no consensus or good quality evidence guiding clinicians in how to treat and how long to treat ASB in pregnancy. The varying course of ASB in combination with the limited evidence for associations with negative long-term effects support the hypothesis that ASB is more likely a commensalism state than a disease. Possibly another not yet identified recognizable latent or early stage for pyelonephritis and/or preterm birth is present. We conclude that the current evidence does not justify a screening programme for asymptomatic bacteriuria to prevent preterm birth or pyelonephritis.