Urinary Tract Infection

The urinary tract is especially vulnerable to infections during pregnancy because the altered secretions of steroid sex hormones and the pressure exerted by the gravid uterus upon the ureters and bladder cause hypotonia and congestion and predispose to urinary stasis. Labor and delivery and urinary retention postpartum also may initiate or aggravate infection. Escherichia coli is the offending organism in over two-thirds of cases.

From 2% to 8% of pregnant women have asymptomatic bacteriuria, which some believe to be associated with an increased risk of prematurity. It is estimated that 20-40% of these women will develop pyelonephritis during pregnancy if untreated.

A first-trimester urine culture is indicated in women with a history of recurrent or recent episodes of urinary tract infection. If the culture is positive, treatment should be initiated as a prophylactic measure. Nitrofurantoin (100 mg twice daily), ampicillin (500 mg four times daily), and cephalexin (500 mg four times daily) are acceptable medications for 3-7 days. Sulfonamides should not be given in the third trimester because they interfere with bilirubin binding and thus impose a risk of neonatal hyperbilirubinemia and kernicterus. Fluoroquinolones are also contraindicated because of their potential teratogenic effects on fetal cartilage and bone. If bacteriuria returns, suppressive medication (one daily dose of an appropriate antibiotic) for the remainder of the pregnancy is indicated. Acute pyelonephritis requires hospitalization for intravenous administration of antibiotics until the patient is afebrile; this is followed by a full course of oral antibiotics.

Delzell JE Jr et al: Urinary tract infections during pregnancy. Am Fam Physician 2000;61:713.