Williams Manual of Pregnancy Complications, 23 ed.

CHAPTER 65. Acute Pyelonephritis

Renal infection is the most common serious medical complication of pregnancy and is responsible for 4 percent of antepartum admissions. Urosepsis is the leading cause of septic shock and may be related to an increased incidence of cerebral palsy in infants born preterm. In most women, infection is caused by bacteria that ascend from the lower tract, facilitated by urine stasis due to pregnancy adaptation. Young age and nulliparity are associated risk factors.


Renal infection is more common after midpregnancy. It is unilateral and right-sided in more than half of cases, and bilateral in a fourth. Symptoms of pyelonephritis include fever, shaking chills, and aching pain in one or both lumbar flank regions and may be accompanied by anorexia, nausea, and vomiting. Although the diagnosis usually is apparent, pyelonephritis may be mistaken for labor, chorioamnionitis, appendicitis, placental abruption, or infarcted myoma, and in the puerperium, for metritis with pelvic cellulitis.


Fever can be as high as 40°C or more and hypothermia as low as 34°C. Tenderness usually can be elicited by percussion in one or both costovertebral angles. The urinalysis often contains many leukocytes, frequently in clumps, and numerous bacteria. Escherichia coli is isolated from the urine or blood in three-fourths of the patients, with Klebsiella pneumoniae, Enterobacter or Proteus isolated in the remaining women.

Almost all clinical findings in these women are ultimately caused by endotoxemia, and so are the serious complications of acute pyelonephritis. A frequent finding is thermoregulatory instability. In addition, acute pyelonephritis may be complicated by a considerable reduction in the glomerular filtration rate that is reversible. Approximately 1 to 2 percent of women with antepartum pyelonephritis develop varying degrees of respiratory insufficiency caused by endotoxin-induced alveolar injury and pulmonary edema. In some women, pulmonary injury is severe, with resultant acute respiratory distress syndrome requiring mechanical ventilation. Endotoxin-induced hemolysis is also common, with about one-third of these women developing acute anemia. Importantly, about 15 percent of women with acute pyelonephritis also have bacteremia.


One scheme for management of the pregnant woman with acute pyelonephritis is shown in Table 65-1. Hospitalization is usually recommended. Outpatient management is possible but is applicable to very few women and mandates close evaluation.

TABLE 65-1. Management of the Pregnant Woman with Acute Pyelonephritis


Intravenous hydration to ensure adequate urinary output is essential. Although we routinely obtain cultures of urine and blood, some clinicians believe this to be of limited clinical utility. Because bacteremia and endotoxemia are common, these women should be watched carefully to detect symptoms of endotoxin shock or its sequelae, and such surveillance is the main reason hospitalization is usually recommended. Urinary output, blood pressure, and temperature are monitored closely. High fever should be treated, usually with acetaminophen and a cooling blanket. This is specially important in early pregnancy because of possible teratogenic effects of hyperthermia.

Pyelonephritis usually responds quickly to intravenous hydration and antimicrobial therapy. The choice of drug is empirical, and ampicillin plus gentamicin, cefazolin, or ceftriaxone has been shown to be 95-percent effective. Ampicillin resistance to E coli has become common, and less than half of strains are sensitive to ampicillin, but most are sensitive to cefazolin. For these reasons, many clinicians prefer to give gentamicin or another amino-glycoside with ampicillin. Serial determinations of serum creatinine are important if nephrotoxic drugs are given. Finally, some prefer cephalosporin or extended-spectrum penicillin, which has been shown to be effective in 95 percent of infected women. The patient may be switched to oral antimicrobials when afebrile and discharged when afebrile for longer than 24 hours. A total course of 7 to 10 days of antibiotics is recommended.

Because changes in the urinary tract induced by pregnancy persist, reinfection is possible. Recurrent infection, both asymptomatic and symptomatic, is common and can be demonstrated in 30 to 40 percent of women following completion of treatment for pyelonephritis unless measures are taken to ensure urine sterility. Nitrofurantoin, 100 mg at bedtime, is given for the remainder of the pregnancy, which reduces recurrence of bacteriuria to 8 percent.

Pyelonephritis Unresponsive to Initial Treatment

In general, clinical symptoms resolve during the first 2 days of therapy, and urine cultures become sterile within the first 24 hours. Almost 95 percent of pregnant women will be afebrile by 72 hours (Figure 65-1). If clinical improvement is not obvious by 48 to 72 hours, then evaluation for urinary tract obstruction should be considered. Pyelocaliceal dilatation, urinary calculi, and possibly an intrarenal or perinephric abscess or phlegmon may be visualized using renal sonography. However, ultrasound is not always successful in localizing these lesions.


FIGURE 65-1 Vital signs graphic chart from a 28-week primigravida with acute pyelonephritis. (From Cunningham FG: Urinary tract infections complicating pregnancy. Clin Obstet Gynecol 1:891, 1988, with permission.)

Therefore, a negative examination should not prompt cessation of the workup in a woman with continuing urosepsis. In some cases, plain abdominal radiography is indicated, because nearly 90 percent of renal stones are radiopaque. Possible benefits far outweigh any minimal fetal risk from radiation. If plain radiography is negative, then a one-shot pyelogram, in which a single radiograph is obtained 30 minutes after contrast injection, usually provides adequate imaging of the collecting system so that stones or structural anomalies can be detected. Magnetic resonance urography may also be used. Passage of a double-J ureteral stent will relieve the obstruction in most cases. If unsuccessful, then percutaneous nephrostomy is done. If this fails, surgical removal of renal stones is required for resolution of infection.

For further reading in Williams Obstetrics, 23rd ed.,

see Chapter 48, “Renal and Urinary Tract Disorders,” and Chapter 5, “Maternal Physiology.”