There are not enough suitable studies available for evaluation to determine whether screening for asymptomatic bacteriuria (ASB) in pregnant women is beneficial or harmful, according to a final report published by the German Institute for Quality and Efficiency in Health Care (IQWiG), which was commissioned by the Federal Joint Committee.

Women who have ASB do not experience symptoms of a urinary tract infection, so it can only be detected through testing—usually via a midstream urine test. Older research indicates that leaving ASB untreated can lead to a kidney infection in about 25% of cases and that a link may also exist between the risk of preterm birth and bacteriuria.

ASB screening is a routine part of antenatal screening due to the presumed benefit of identifying infection. For the new report, researchers identified three studies published between 1960 and 1969 that evaluated neonatal morbidity, pyelonephritis, and lower urinary tract infection. However, because the studies were more than 40 years old, the findings are not applicable to today’s healthcare situations. Study participants at that time underwent measures that are no longer used in healthy pregnant women, and it is unclear how ASB was diagnosed.

Also, interpretation of these older study results was difficult because the main characteristics of the study populations is not included in the results, and potential harm from the antibiotics commonly used in the 1960s was not evaluated. Different antibiotics are used now to treat ASB, so the benefit-harm ratio may have tipped, either in favor of screening or in favor of watchful waiting. “The question of whether pregnant women or their children benefit from screening is therefore just as unclear as the question of whether they benefit from antibiotic treatment of ASB detected by screening,” according to a press release.

ASB screening is only recommended for high-risk groups in the Netherlands, so it is possible to conduct research there that assesses how unscreened control groups do overall. An ongoing study in the Netherlands found that pyelonephritis and preterm birth occurred less often than expected—meaning there was a “markedly decreased incidence of upper urinary tract infections,” according to a press release. This could indicate that pregnant women with ASB in today’s world experience fewer complications—which could change the thinking on the advantages and disadvantages of screening.

"The question as to how beneficial a general screening for ASB in pregnant women is should also be posed again in Germany,” Stefan Sauerland, head of IQWiG's non-drug intervention department, said in a prepared statement. "Such a study would be feasible and ethically justifiable if one excluded certain high-risk groups so that antibiotic treatment would not be withheld from them in the placebo arm.”