Asymptomatic bacteriuria (ASB) is the presence of bacteria in the urine without concomitant specific urinary tract symptoms. The incidence is not influenced by pregnancy, and the prevalence remains 2% to 7% of all pregnancies, similar to the nonpregnant population, and tends to be more evident in the first trimester (2,3). Certain groups do appear to be at higher risk for ASB. These include patients with lower socioeconomic status, sickle cell trait and disease, diabetes, and chronic urinary retention (2,3,4,5,6,7,8). The American College of Obstetrics and Gynecology (ACOG) recommends routine screening for bacteriuria at the first prenatal visit. Recently, the US Preventive Services Task Force (USPSTF) reaffirmed screening for ASB in pregnant women by urine culture at the first prenatal visit or at 12 to 16 weeks’ gestation (9).

The diagnosis is made by bacterial culture revealing >10⁵ organisms of a single species per milliliter of urine without specific UTI symptoms. Because pyelonephritis may occur with lower colony counts (20k to 50k) in the presence of symptoms or specific isolates such as group B streptococcus or Escherichia coli should be considered positive findings, and patients should be provided treatment based on sensitivity of isolates. A single midstream clean-catch urine culture suffices for the diagnosis. E. coli, Klebsiella, and Enterobacter species account for more than 85% of the isolates. Group B streptococcus, although a rare isolate, when identified in the urine, should be aggressively treated to prevent transmission to the neonate and frank progression to pyelonephritis. This patient will also require intrapartum GBS prophylaxis.

By identifying and treating ASB, a significant reduction in symptomatic infections can be achieved. Left untreated, approximately 40% of all cases of ASB will progress to acute symptomatic infection and 25% to acute pyelonephritis (AP) and its increased attendant morbidity. With adequate therapy, the risk is significantly decreased to only 3% (3,4).

Therapy should be directed by specific isolate identification and sensitivity; some authorities do not recommend C&S evaluation on initial positive cultures in uncomplicated pregnant individuals. Drugs that provide successful ASB treatment and have safe fetal profiles include sulfa-based drugs, first-generation cephalosporins, nitrofurantoin, and penicillin-based alternatives. The latter group should not be used empirically but rather for specific isolates with documented sensitivity because E. coli has high resistance to penicillin derivatives. It should be remembered that due to increased prevalence of antibiotic resistance the practitioner should use a community accepted first-line agent that presumes adequate coverage and then follow up with specific agents if culture and sensitivity dictates otherwise. In some areas of the country, up to a third of strains have resistance to penicillins and sulfonamides. Nitrofurantoin and trimethoprim-sulfamethoxazole have geographic resistance rates of 5% to 20%. Typically, in pregnant individuals, single-dose therapy is discouraged. A prolonged course of 7 days is recommended in this population with shorter duration of 3 days being reserved for nonpregnant patients. Suggested drug regimens are presented in Table 9.1. After completion of treatment, a test of cure culture should be obtained, because as many as one third of patients will have persistent bacteriuria. When persistence is confirmed, longer courses and/or suppressive therapy may be prudent.

AP disorder complicates more than 1% to 2.5% of all pregnancies (10). Forty percent of pregnant women with AP have antecedent symptoms of lower UTI. Unlike ASB and AC, pregnancy does seem to predispose to AP. Two thirds of cases arise in women with previously documented positive urine culture results and the remainder arise de novo. Most cases of AP in pregnant women occur in the second and third trimesters when significant and maximal physiologic changes have occurred (4,10). The disease is thought to result from the significant physiologic changes of the genitourinary system, namely, urethral dilation, mechanical obstruction of the gravid uterus, and significant glucosuria and aminoaciduria.

The diagnosis of AP is based on the presence of systemic signs and symptoms that include fever, chills, nausea, vomiting, and costovertebral angle tenderness. Almost always, these cases are complicated by a fever and, in some cases, significant temperature elevation may occur ≥44°C (11). Costovertebral sensitivity tends to be right sided in the predominance of cases but does not exclude the possibility of bilateral or left-sided tenderness.

Laboratory findings usually include an elevated white blood cell count, but occasionally, in mild or early infections, this may be normal. Some investigators have reported decreased hematocrit and transient renal dysfunction (10,12). Significant pyuria, hematuria, and ultimately positive urine cultures are mainstay findings. It is not unusual for a patient to have “sterile” urine despite having classic symptoms. When confronted with this clinical scenario, treatment should not be postponed.

Effects of AP are not limited to the kidney. These include hemolytic anemia, renal dysfunction, and pulmonary dysfunction including transient mild distress to frank adult respiratory distress syndrome (13,14). About 15% to 20% of women with AP also have bacteremia (2). As with any systemic infection combining with the immunocompromised status of pregnancy, septic shock may result. Unlike ASB and AC, AP is associated with increased occurrence of uterine contractions and preterm labor.

The treatment of pyelonephritis consists of aggressive systemic intravenous antibiotics and judicious fluid management. All pregnant patients suspected of having pyelonephritis should be admitted to the hospital for treatment. The initial antimicrobial selection should be reflective of most common isolates and should be cost sensitive. Several regimens can be employed. These include gentamicin and ampicillin or first- or third-generation cephalosporins. A randomized controlled trial showed 95% efficacy of these regimens (15). This selection of the third-generation cephalosporins allows for the possibility of early discharge and outpatient therapy in gestations <20 weeks and absent complicating medical conditions (16). Significant cost savings have also been achieved with daily single-dose ceftriaxone use versus multi-dose regimens during inpatient therapy (17).

With antibiotic therapy selection, clinical resolution generally should be realized in 24 to 48 hours. If improvement is not achieved in 48 to 72 hours, clinical suspicion should be heightened, and a diligent search for other causes (e.g., renal calculi, abscess, or obstruction) commenced. Therapy should be continued until the patient is afebrile for 48 to 72 hours. A test of cure is mandatory. Up to 25% of patients will have recurrent pyelonephritis (10). This observation has led most authorities to recommend suppressive therapy for the duration of the pregnancy (18). The agent selected should differ from the treating agent, should be cost sensitive, and should have minimal normal flora impact. Therapeutic suggestions are provided in Table 9.1.