Pregnancy causes numerous changes in the woman’s body. Hormonal and mechanical changes increase the risk of urinary stasis andvesicoureteral reflux. These changes, along with an already short urethra (approximately 3-4 cm in females) and difficulty with hygiene due to a distended pregnant belly, increase the frequency of urinary tract infections (UTIs) in pregnant women. Indeed, UTIs are among the most common bacterial infections during pregnancy.

In general, pregnant patients are considered immunocompromised UTI hosts because of the physiologic changes associated with pregnancy (see Pathophysiology). These changes increase the risk of serious infectious complications from symptomatic and asymptomatic urinary infections even in healthy pregnant women.

Oral antibiotics are the treatment of choice for asymptomatic bacteriuria and cystitis. The standard course of treatment for pyelonephritis is hospital admission and intravenous antibiotics. Antibiotic prophylaxis is indicated in some cases. (See Treatment of UTI in Pregnancy andUrethral Catheterization in Women.) Patients treated for symptomatic UTI during pregnancy should be continued on daily prophylactic antibiotics for the duration of their pregnancy.

Annual health costs for UTI exceed $1 billion. Although the condition-specific cost of asymptomatic bacteriuria or UTI in pregnancy is unknown, screening for these conditions in pregnant women is cost-effective as compared with treating UTI and pyelonephritis without screening. Goals for future research include targeting low-income groups and women in developing countries for screening and early treatment, as well as determining whether a causal relation exists between maternal UTI and childhood neurologic consequences.

For patient education information, see the Kidneys and Urinary System Center and Pregnancy and Reproduction Center, as well as Urinary Tract Infections, Pregnancy, Bladder Control Problems, and Blood in the Urine.

Definitions of key terms

Urinary tract infection

UTI is defined as the presence of at least 100,000 organisms per milliliter of urine in an asymptomatic patient, or as more than 100 organisms/mL of urine with accompanying pyuria (>7 white blood cells [WBCs]/mL) in a symptomatic patient. A diagnosis of UTI should be supported by a positive culture for a uropathogen, particularly in patients with vague symptoms. UTIs are associated with risks to both the fetus and the mother, including pyelonephritis, preterm birth, low birth weight, and increased perinatal mortality.

Asymptomatic bacteriuria

Asymptomatic bacteriuria is commonly defined as the presence of more than 100,000 organisms/mL in 2 consecutive urine samples in the absence of declared symptoms. Untreated asymptomatic bacteriuria is a risk factor for acute cystitis (40%) and pyelonephritis (25-30%) in pregnancy. These cases account for 70% of all cases of symptomatic UTI among unscreened pregnant women.

Acute cystitis

Acute cystitis involves only the lower urinary tract; it is characterized by inflammation of the bladder as a result of bacterial or nonbacterial causes (eg, radiation or viral infection). Acute cystitis develops in approximately 1% of pregnant patients, of whom 60% have a negative result on initial screening. Signs and symptoms include hematuria, dysuria, suprapubic discomfort, frequency, urgency, and nocturia. These symptoms are often difficult to distinguish from those due to pregnancy itself.

Acute cystitis is complicated by upper urinary tract disease (ie, pyelonephritis) in 15-50% of cases.

Acute pyelonephritis