Asymptomatic bacteriuria and urinary tract infections in pregnancy – a review of the literature

Abstract

Background. The approach to the management of asymptomatic bacteriuria (AB) and urinary tract infections (UTIs) in pregnancy, including the choice of antibiotics, is not always straightforward. Aims. The aim of this article is to review the literature on AB and UTI in pregnancy and to discuss the findings. Materials and method. Various internet search engines were used to identify references regarding pregnancy-associated AB and UTI, which formed a framework for the literature review. Results. Both conditions were found to be common in pregnancy. Pregnancy-associated UTI is defined as either a lower urinary tract infection (acute cystitis) or an upper urinary tract infection (acute pyelonephritis). The approach to the management of pregnancy-associated AB and UTI presents a complex issue, including the choice of antibiotics. UTIs occur when there are at least 100 000 organisms present per ml of urine in an asymptomatic patient, or more than 100 organisms per ml of urine with accompanying pyuria (more than seven white blood cells per ml in a symptomatic patient). A diagnosis of UTI requires a positive culture and identification of the pathogen, especially in patients with vague symptoms. UTIs are associated with risks to both the mother and the fetus, including pyelonephritis, preterm birth, low birthweight and increased risk of perinatal mortality. AB occurs when the bacterial count is greater than 100 000 organisms per ml in two consecutive samples of urine and in the absence of declared symptoms. If AB remains untreated during pregnancy, the risk of developing cystitis is 40% and the risk of developing pyelonephritis is 25–30%. The tendency for AB to progress to pyelonephritis is higher in pregnant women than in non-pregnant women and is associated with an increased risk of preterm birth, low birthweight and perinatal mortality. Appropriate short-term antibiotic courses are recommended for both pregnant and non-pregnant women. Short-term courses of any of the following treatments have been recommended to minimize antimicrobial exposure to the fetus. The prognosis of the majority pregnant women with UTI or AB during pregnancy is good. Most long-term sequelae are due to complications associated with septic shock, respiratory failure or hypotensive hypoxia with extreme gangrene. UTIs associated with pregnancy have few direct sequelae in view of the fact that fetal bloodstream infection is rare; nevertheless, uterine hypoperfusion due to maternal dehydration, maternal anaemia and direct bacterial endotoxin damage to the placental vasculature may result in fetal cerebral hypoperfusion. Untreated upper UTIs in pregnant women are associated with low birthweight, prematurity, premature labour, hypertension, pre-eclampsia, maternal anaemia and amnionitis. UTIs which occur during pregnancy are associated with intrauterine growth retardation, pre-eclampsia, preterm delivery and caesarean delivery. Conclusions. In order to avoid or minimize complications that may be associated with AB and UTI during pregnancy, both should be appropriately treated. Several antibiotic treatments are available and details of the antibiotic therapies are discussed below.