Pregnant women are predisposed to urinary tract infections (UTIs) due to the stasis of urine in the dilated collecting system and changes in urinary composition with glucosuria and aminoaciduria. Approximately 2–10 % of pregnancies develop asymptomatic bacteriuria, and if untreated, up to 30 % of these women will develop pyelonephritis. Low birth weight and preterm delivery are associated with asymptomatic bacteriuria, but treatment with antibiotics decreases both the incidence of pyelonephritis (OR 0.23, 95 % CI 0.13–0.41) and low birth weight [2]. Asymptomatic bacteriuria and UTI have similar associated complications. Organisms infecting the urinary tract in pregnancy are the same as in nonpregnant patients with the most common organism being E. coli. Other pathogens include Klebsiella, Enterobacter, Proteus, and gram-positive organisms. Treatment is best guided by local microbiology data and susceptibilities and consists of 3–7 days of antibiotics with a follow-up test of cure 1 week after antibiotic completion. Monthly urine cultures are indicated for the remainder of the pregnancy due to the high likelihood of recurrence of asymptomatic bacteriuria and UTI. See Table 12.2 for suggested antibiotic regimens for treatment, but the fluoroquinolones should be avoided in pregnancy and breastfeeding. If a recurrent episode of asymptomatic bacteriuria or UTI occurs, suppressive or prophylactic therapy is recommended to prevent recurrence. See Table 12.3.

Pyelonephritis in pregnancy is associated with significant maternal and fetal morbidity including bacteremia and sepsis, acute respiratory distress syndrome (ARDS), and preterm labor and delivery. Approximately 8 % of pyelonephritis is associated with pulmonary edema [3, 4] suggesting that close monitoring of oxygen saturation and fluid status is prudent. Given these potential complications, pyelonephritis should be treated as an inpatient in pregnant women. Suggested intravenous regimens can be found in Table 12.4. After clinical improvement, gravidas with pyelonephritis can be changed to an oral regimen based on culture and sensitivity results to complete a 10–14-day course. Recurrence of pyelonephritis in the same pregnancy occurs in 6–8 % of women but can be prevented with prophylactic antibiotics [5, 6]. See Table 12.3.

Renal stones occur in approximately 1 in 200 to 1 in 1,500 pregnancies [7]. The physiologic changes predisposing women to UTI in pregnancy also predispose women to the development of renal calculi. In addition to stasis and an increase in excretion of calcium, uric acid, and oxalate, there is a decrease in pH favoring stone formation. The most common stones in pregnancy are calcium phosphate in distinction to calcium oxalate stones which are more common in nonpregnant patients. Flank pain and hematuria are a typical presentation. Though spiral CT to diagnose renal stones involves a radiation dose within an acceptable range for pregnant women, this is ideally avoided. Renal ultrasound can be done initially but may only identify 60 % of stones. A transvaginal ultrasound may be useful to identify distal stones. Magnetic resonance urography (MRU) can be used as a second-line test if it is available. Women may be initially treated for pain with narcotics while awaiting spontaneous passage of the stone. Whether medical expulsive therapy would be useful in pregnancy when there already is a dilated renal collecting system is unclear, but if considered, calcium channel blockers such as nifedipine can be used. On the other hand, there is no data on the use of tamsulosin in pregnant women. If intervention is indicated such as with the presence of renal insufficiency or failure of conservative treatment, ureteroscopy with stone removal can be done safely during pregnancy. Other temporizing procedures that may be considered include placement of ureteral stents or nephrostomy tubes. Lithotripsy is not recommended in pregnancy, however. Suggested laboratory evaluation includes electrolytes with calcium, BUN, creatinine, and complete blood count, as well as straining of urine and chemical analysis of any collected stones.

The etiologies of acute renal failure in pregnancy are the same as those in nonpregnant patients with additional causes specific to pregnancy. The more common pregnancy-related causes include obstetric hemorrhage; placental abruption; severe preeclampsia or hemolysis, elevated liver enzymes, low platelet (HELLP) syndrome; and septic abortion. A more complete differential diagnosis is outlined in Table 12.5. Preeclampsia must be strongly considered in any pregnant women after 20 weeks gestation either as a primary cause of renal dysfunction or as a cause superimposed on another underlying renal disease. Forty percent of acute renal insufficiency in pregnancy is caused by preeclampsia in developed countries [8]. The thrombotic microangiopathies (TMA) such as thrombotic thrombocytopenic purpura–hemolytic uremic syndrome (TTP–HUS) appear to be associated with pregnancy and can often be difficult to distinguish from preeclampsia/HELLP syndrome and acute fatty liver of pregnancy (AFLP). Approximately 10 % of women who develop TTP–HUS do so in association with pregnancy or the postpartum period [9, 10]. When the distinction is unclear, treatment should be targeted at both preeclampsia/HELLP and TTP–HUS with delivery and plasma exchange.

The workup of acute renal insufficiency in pregnancy is the same as in nonpregnant patients. History often offers significant clues especially if there are signs and symptoms of obvious disorder such as bleeding, sources of infection or sepsis, or collagen vascular disease. The urine sediment should be examined for evidence of nephritis or acute tubular necrosis (ATN). Renal ultrasound can rule out obstruction which has been reported in rare cases and may also identify evidence for underlying renal disorders. In some cases serologic studies such as ANA, ANCA, antiGBM, and complement levels will be helpful. Because it is difficult to rule out whether preeclampsia is contributing, it is in both maternal and fetal interests to deliver women with worsening creatinine at or near term. In women remote from term, the decision to deliver a premature infant is more complicated. If a clinical diagnosis cannot be made, renal biopsy can be considered when it will provide guidance for possible treatment that will allow pregnancy to be prolonged while a primary maternal disorder is treated. Renal biopsy can be done safely in pregnancy [11] though there are conflicting reports about whether the risk for bleeding is increased [12].