Urinary Tract Disorders during pregnancy

URINARY TRACT DISORDERS

Urinary tract infections (UTIs) are common in preg-nancy. Approximately 8% of all women (pregnant and non-pregnant) have >10⁵ colonies of a single bacterial species on a midstream culture. Approximately 25% of the pregnant women in this group develop an acute, symptomatic UTI. Other urinary tract disorders that may complicate preg-nancy include urinary calculi, nephrolithiasis, and pre-existing renal disease.

Asymptomatic Bacteriuria and Uncomplicated Urinary Tract Infection

Compared with nonpregnant women with similar colony counts on urine culture, asymptomatic bacteriuria in pregnancy is more likely to lead to cystitis and pyelonephritis.The increasedincidence of symptomatic infection during pregnancy is thought to be caused by pregnancy-associated urinary sta-sis and glucosuria. This relative urinary stasis in pregnancy is a result of progesterone-induced decreased ureteral tone and motility, mechanical compression of the ureters at the pelvic brim, and compression of the bladder and ureteral orifices. In addition, the pH of the urine is increased because of increased bicarbonate excretion, which also enhances bacterial growth.

A urine culture is obtained at the onset of prenatal care and patients with asymptomatic bacteriuria are treated with ampicillin, cephalexin or nitrofurantoin.

The most common organism identified is Escherichia coli. Approximately 25% to 30% of patients not treated for asymptomatic bacteriuria proceed to symptomatic UTI; hence, this treatment should prevent a significant num-ber of symptomatic UTIs in pregnancy. However, 1.5% of patients with initial negative cultures also develop symptomatic UTIs during pregnancy. Suppressive anti-microbial therapy is indicated if there are repetitive UTIs during pregnancy or following pyelonephritis during preg-nancy. Consideration should be given to postpartum ra-diographic evaluation of these patients to identify renal parenchymal and urinary-collecting duct abnormalities.

Acute cystitis occurs in approximately 1% of preg-nancies, and can manifest with dysuria, urinary frequency, and/or urgency. The treatment is the same as for asymp-tomatic bacteriuria.

Pyelonephritis

Patients with pyelonephritis (inflammation of the renal parenchyma, calices, and pelvis) are acutely ill, with fever, costovertebral tenderness, general malaise, and often dehydration. Approximately 20% of these ill patients demonstrate increased uterine activity and preterm labor, and approximately 10% have positive blood cultures if they are obtained in the acute febrile phase of the disease. Pyelonephritis occurs in 2% of all pregnant patients and is one of the most common medical complications of pregnancy requir-ing hospitalization, especially in its context as a major cause of maternal mortality (septic shock).

After urinalysis and urine culture are obtained, patients are treated with intravenous hydration and antibiotics, commonly a cephalosporin or ampicillin and gentamicin. Uterine contractions may accompany these symptoms, and specific tocolytic therapy may be required if preterm labor ensues. It is known that E. coli can produce phospholipase A, which in turn can promote prostaglandin synthesis, result-ing in an increase in uterine activity. Fever is also known to induce contractions, so antipyretics are required for a tem-perature >100.4°F. Attention must be paid to the patient’s re-sponse to therapy and her general condition; sepsis occurs in 2% to 3% of patients with pyelonephritis, and adult respiratory distress syndrome can occur. If improvement does not occur within48 to 72 hours, urinary tract obstruction or urinary calculus should be considered, along with a reevaluation of antibiotic coverage. Ultrasonography or other imaging study such as computed tomography will sometimes identify a calculus or abscess. The organisms most commonly cultured from the urine of symptomatic pregnant patients are E. coli and other gram-negative aerobes. Follow-up can be with either fre-quent urine cultures and/or empiric antibiotic suppression with an agent such as nitrofurantoin.

Recurrent symptoms or failure to respond to usual therapy suggests another cause for the findings. In these patients, a complete urologic evaluation 6 weeks after pregnancy may be warranted.

Nephrolithiasis and Urinary Calculi

Urinary calculi are identified in approximately 1 in1500 patients during pregnancy, although pregnancy per se does not promote stone development. Symptoms simi-lar to those of pyelonephritis but without fever suggest urinary calculi. Microhematuria is more common with this condition than in uncomplicated UTI. Renal colic(pain) is a typical symptom in nonpregnant women, but is seen less frequently in pregnant women because of the hormone-induced relaxation of ureteral tone. Usually, hydration andexpectant management, along with straining of urine in search of stones, suffice as management. Occasionally, however, the presence of a stone can lead to infection or complete obstruction, which may require urology consul-tation and drainage by either ureteral stent or percuta-neous nephrostomy.

Preexisting Renal Disease

During preconception counseling, patients who have pre-existing renal disease (chronic renal failure or transplant) should be advised of the significant risks involved in a pregnancy. Pregnancy outcome is related to the degree of serumcreatinine elevation and the presence of hypertension.

Overall, pregnancy does not seem to have a negative impact on mild chronic renal diseases. In general, patients with mildrenal impairment (serum creatinine <1.5 mg/dL) have rel-atively uneventful pregnancies, provided other complica-tions are absent. Patients with moderate renal impairment (serum creatinine 1.5 to 3.0 mg/dL) have a more guarded prognosis with an increased incidence of deterioration of renal function. Patients with severe renal impairment have the worst outcome. In approximately 50% of patients with renal disease, proteinuria is noted. An increase in pro-teinuria during pregnancy is not, by itself, a serious con-sequence. Many patients with renal disease also have preexisting or concurrent hypertension. These women are at increased risk for hypertensive complications of pregnancy.

In addition to hypertension, there is an increased incidence of intrauterine growth restriction in patients with chronic renal disease. Serial assessments of fetal well-being andgrowth are frequently performed. Pregnancy following renal transplantation is generally associated with a good prognosis if at least 2 years have elapsed since the transplant was performed, and thorough renal assessment reveals no evidence of active disease or rejection. Drug therapy should be minimal.