Urinary Tract Infection (UTI) in Pregnancy

Background

• Urinary tract infections (UTIs) are common, occurring in about 2-10% of pregnancies.
  • Symptomatic infections are classified as cystitis (lower tract infections) and pyelonephritis (upper tract infections).
  • Asymptomatic bacteruria (ASB) refers to the presence of bacteria in the urine in the absence of symptoms.
• Due to multiple physiologic factors in pregnancy such as an enlarging uterus compressing the bladder, ureteral dilatation and decreased ureteral peristalsis, the presence of bacteriuria in pregnancy is associated with increased risk of ascending infection and pyelonephritis.
• Though the overall risk of pyelonephritis is low (about 0.7%) in pregnancy, the presence of ASB increases that risk to about 2.5%.
• To reduce the rate of pyelonephritis and its complications, pregnancy is one of the rare instances in which screening and treatment for asymptomatic bacteriuria is recommended by many medical societies, the evidence supporting this approach is of low-quality.
• Other adverse outcomes potentially associated with asymptomatic bacteriuria and UTIs in pregnancy include preeclampsia, preterm delivery, intrauterine growth restriction, and low birth weight.

Evaluation

• The Infectious Disease Society of America and the United States Preventive Task Force recommend screening for all pregnant women by urine culture at least once early in pregnancy (Strong recommendation).
• The diagnosis of ASB is made when ≥ 10⁵ colony-forming units (CFU)/mL of a single bacterial strain isolated from 2 consecutive voided urine specimens.
• Urine culture is also needed for diagnosis of acute cystitis or pyelonephritis, and to guide therapy in pregnant women with signs and symptoms of acute cystitis or pyelonephritis.
  • For cystitis:
    • presence of symptoms of lower urinary tract infection, such as dysuria, frequency, and urgency, plus
    • isolation of ≥ 1,000 CFU/mL from midstream clean-catch urine culture
  • For pyelonephritis:
    • presence of signs and symptoms of upper tract infection such as fever and flank pain, plus
    • isolation of ≥ 1,000 CFU/mL from midstream clean-catch urine culture
• Consider ultrasound or magnetic resonance imaging (MRI) if complicating factors such as a urinary tract obstruction or stone are suspected (Weak recommendation).
• Consider blood cultures for women in whom bacteremia or sepsis is suspected.

Management

• No single antibiotic has been shown to be superior to another for the treatment of UTI in pregnancy.
• Common options for treating asymptomatic bacteriuria and acute cystitis in pregnancy include:
  • amoxicillin 500 mg every 8 hours for 3-7 days
  • amoxicillin-clavulanate 500 mg every 12 hours for 3-7 days
  • cephalexin 500 mg every 8 hours for 3-7 days
  • fosfomycin 3 g as single dose
• Common options for treating pyelonephritis in pregnancy include:
  • ceftriaxone 1-2 g IV or intramuscularly once daily
  • aztreonam 1 g IV every 8-12 hours
  • piperacillin-tazobactam 3.375-4.5 g IV every 6 hours
  • cefepime 1 g IV every 12 hours
  • imipenem-cilastatin 500 mg IV every 6 hours
  • ampicillin 2 g every 6 hours plus gentamicin 3-5 mg/kg/day IV in 3 divided doses
• Choice of empiric antibiotic should take local epidemiology into consideration and definitive therapy should be tailored to the culture and susceptibility results.
• Unlike in nonpregnant women, cotrimoxazole and nitrofurantoin are generally avoided, particularly in the first and third trimester, when alternatives exist due to risk of adverse events.
• For pyelonephritis, IV therapy can be switched to oral therapy with an appropriate agent after clinical improvement to complete a total 7-14 day course (Weak recommendation).
• Consider test of cure following treatment.