Screening and Treating Pregnant Women with Asymptomatic Bacteriuria May Not Be Helpful

EBM Focus - Volume 10, Issue 50

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Reference - Lancet Infect Dis 2015 Nov;15(11):1324 (level 2 [mid-level] evidence)

  • Current United States guidelines recommend screening and treating pregnant women with asymptomatic bacteriuria to prevent pyelonephritis, preterm birth, and low birth weight, but the evidence supporting these recommendations is weak.
  • A new cohort study with an embedded randomized trial found a small increase in incidence of pyelonephritis in women with untreated asymptomatic bacteriuria compared to women with negative urine cultures, however the absolute risk was small.
  • As a result of the lack of quality evidence suggesting a benefit, the European Association of Urology has recently updated their guideline to make no recommendation on screening or treating pregnant women with asymptomatic bacteriuria.

The Infectious Disease Society of America (IDSA) and the United States Preventative Services Task Force (USPSTF) both strongly recommend screening all pregnant women for asymptomatic bacteriuria with urine culture around 12-16 weeks gestation and treating women with positive urine cultures with antibiotics (Clin Infect Dis 2005 Mar 1;40(5):643, Ann Intern Med 2008 Jul 1;149(1):43). These recommendations are based on a Cochrane review finding that antibiotic treatment of asymptomatic bacteriuria in pregnant women was associated with a decreased incidence of maternal pyelonephritis as well as a reduced risk of preterm birth and low birthweight (Cochrane Database Syst Rev 2015 Aug 7;(8):CD000490). The quality of evidence included in the Cochrane review is poor, however. All included trials were published before 1987, with 9 of the 14 trials published between 1960 and 1969 when methods for determining gestational age were less accurate. In addition, most of the trials treated women with positive urine cultures with antibiotics that are no longer used for pregnant women and for durations far exceeding the current IDSA recommendation of 3-7 days and only 1 trial reported treatment-related adverse events. Due to this low quality of evidence, a recent cohort study with an embedded randomized trial was performed to assess the need for screening and treating pregnant women for asymptomatic bacteriuria.

A total of 4,283 women (mean age 31 years) with singleton pregnancies at 16-22 weeks gestation were screened for asymptomatic bacteriuria at 13 centers in the Netherlands and 248 women (5.8%) had positive urine cultures from a single dipslide. Eighty-five women with asymptomatic bacteriuria were then randomized to nitrofurantoin 100 mg vs. placebo twice daily for 5 days. The remaining 163 women with asymptomatic bacteriuria declined trial participation because they did not want to receive antibiotics for an asymptomatic condition, but all women were followed until 6 weeks postpartum. There were no significant differences in the rates of pyelonephritis or delivery at < 34 weeks comparing women with asymptomatic bacteriuria treated with nitrofurantoin to women treated with placebo or refusing treatment (see table below). Comparing untreated or placebo treated women with asymptomatic bacteriuria to women screening negative for bacteriuria, women with asymptomatic bacteriuria had a significantly higher rate of pyelonephritis, but no significant difference in the rate of deliveries at < 34 weeks. Furthermore, while women with untreated asymptomatic bacteriuria had significantly higher rates of symptomatic urinary tract infection (20.2%) and recurrent urinary tract infection (8.7%) treated with antibiotics during pregnancy compared to women with negative screenings (7.9% and 2.6%, respectively), there were no significant differences in other adverse maternal or neonatal outcomes.

Although pregnant women with untreated asymptomatic bacteriuria had a slightly higher risk of developing pyelonephritis compared to women without bacteriuria, the absolute risk was small and the subsequent disease course was mild. The increase in pyleonephritis as well as that of uncomplicated urinary tract infections did not influence the development of other adverse maternal or neonatal outcomes; however, this study was not large enough to detect differences in most of these outcomes due to low event rates. These results suggest that screening for asymptomatic bacteriuria may not clearly lead to better pregnancy-related outcomes for all and exposes a large number of women to unnecessary antibiotics. Overall, these findings call into question recommendations for routine screening of all pregnant women and for treatment of asymptomatic women, particularly in the climate of growing antimicrobial resistance. Indeed, the European Association of Urology has recently updated its guidelines to make no recommendation for screening or treating pregnant women with asymptomatic bacteriuria based on the lack of benefit derived in this study combined with the low quality of the evidence for benefit in previous studies (EAU 2015 Mar).

For more information, see the Urinary tract infection (UTI) in pregnancy and Asymptomatic bacteriuria topics in DynaMed Plus. DynaMed users click here and here.


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