URINARY TRACT INFECTIONS COMPLICATING PREGNANCY

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PHYSIOLOGY

The female urethra is relatively short (3–4 cm in length) and is located in close proximity to the vagina, which is colonized with organisms from the gastrointestinal tract. The uropathogens most commonly isolated in ASB are similar to those in cystitis and pyelonephritis. Escherichia coli is the primary pathogen in 65% to 80% of cases. Other pathogens include Klebsiella pneumoniae, Proteus mirabilis, Enterobacter species, Staphylococcus saprophyticus, and Group B beta-hemolytic streptococcus (

BACTERIAL VIRULENCE

The concept of bacterial virulence is important in urinary tract infections. The presence or absence of certain virulence factors may determine why some women with ASB develop pyelonephritis and others do not. Some uropathogens have the ability to adhere to the uroepithelium; this capacity is mediated by the presence of adhesins on the bacterial surface. E. coli have several different adhesins known as pill or fimbriae. Some E. coli express one group of adhesins known as P-fimbriae, which

ASYMPTOMATIC BACTERIURIA

ASB is defined as persistent bacterial colonization of the urinary tract without urinary tract symptomatology. ASB occurs in 5% to 10% of pregnant women.59 The prevalence of the condition in pregnancy is similar to that seen in nonpregnant women; therefore, pregnancy is not believed to be a predisposing factor in the development of bacteriuria.1 The prevalence of ASB is inversely related to socioeconomic status and is markedly elevated in indigent populations.37 Patients with sickle cell

CYSTITIS

Acute bacterial cystitis complicates 0.3% to 1.3% of pregnancies.26,54 There is a paucity of literature on cystitis in pregnancy; currently, the only documented morbidity of cystitis in pregnancy is the discomfort associated with the infection. It is not known whether cystitis increases rates of preterm birth, low birthweight, or pyelonephritis. Antepartum surveillance programs designed to eradicate ASB have no effect on the incidence of cystitis; therefore, it appears that most cases of

ACUTE PYELONEPHRITIS

Acute pyelonephritis occurs in 1% to 2% of all pregnancies. The population incidence varies and depends on the prevalence of ASB in the commtmity and whether patients with ASB are routinely treated. Women with a history of pyelonephritis, urinary tract malformations, or renal calculi are at an increased risk for the development of pyelonephritis. In a prospective study of 656 women with pyelonephritis, 73% of cases were identified in the antepartum period, 8% were diagnosed intrapartum, and 19%

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    Address reprint requests to Lynnae K. Millar, MD Fetal Diagnostic Center Kapiolani Medical Center for Women and Children 1319 Punahou Street, Suite 540 Honolulu, Hawaii 96826

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