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Urinary tract infections and asymptomatic bacteriuria in pregnancy

Thomas M Hooton, MD
Kalpana Gupta, MD, MPH
Section Editors
Stephen B Calderwood, MD
Charles J Lockwood, MD, MHCM
Deputy Editor
Allyson Bloom, MD


Urinary tract infections (UTIs) are common in pregnant women. By convention, UTI is defined either as a lower tract (acute cystitis) or upper tract (acute pyelonephritis) infection. UTIs (acute cystitis and pyelonephritis) and asymptomatic bacteriuria in pregnant women will be reviewed here.

Issues related to urinary tract infections or asymptomatic bacteriuria in other populations are discussed in detail elsewhere. (See "Acute uncomplicated cystitis and pyelonephritis in women" and "Acute uncomplicated cystitis and pyelonephritis in men" and "Acute complicated cystitis and pyelonephritis" and "Approach to the adult with asymptomatic bacteriuria" and "Asymptomatic bacteriuria in patients with diabetes mellitus" and "Catheter-associated urinary tract infection in adults".)


Incidence and risk factors — The incidence of bacteriuria in pregnant women is approximately the same as that in nonpregnant women, however, recurrent bacteriuria is more common during pregnancy. Additionally, the incidence of pyelonephritis is higher than in the general population, likely as a result of physiologic changes in the urinary tract during pregnancy. (See 'Pathogenesis' below.)

Asymptomatic bacteriuria occurs in 2 to 7 percent of pregnant women [1,2]. It typically occurs during early pregnancy, with only approximately a quarter of cases identified in the second and third trimesters [3]. Factors that have been associated with a higher risk of bacteriuria include a history of prior urinary tract infection, pre-existing diabetes mellitus, increased parity, and low socioeconomic status [4-6].

Without treatment, as many as 30 to 40 percent of pregnant women with asymptomatic bacteriuria will develop a symptomatic urinary tract infection (UTI), including pyelonephritis, during pregnancy [7]. This risk is reduced by 70 to 80 percent if bacteriuria is eradicated (see 'Rationale for treatment' below). Although a study from the Netherlands suggested a low rate of pyelonephritis among 208 women with untreated asymptomatic bacteriuria (2.4 percent versus 0.6 percent among 4035 women without bacteriuria), this study included only low-risk women with uncomplicated singleton pregnancies without diabetes mellitus or urinary tract abnormalities, and it is uncertain whether these results are generalizable [8].

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Literature review current through: Nov 2017. | This topic last updated: Aug 24, 2017.
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