Urinary tract infections in pregnancy

Definition

• Urinary tract infections in pregnancy comprise asymptomatic bacteriuria, cystitis and pyelonephritis; asymptomatic bacteriuria may progress to symptomatic cystitis or pyelonephritis.
• Asymptomatic bacteriuria is a significant bacterial count in the urine without symptoms of lower or upper urinary tract infection; studies usually use a threshold of at least 10⁵ colony-forming units per millilitre in midstream urine.

Occurrence & epidemiology

Epidemiology

• Urinary tract infections are more common in pregnancy and are reported in about 18% of pregnancies; asymptomatic bacteriuria has a prevalence of 2–10% in premenopausal women.

Aetiopathogenesis

Aetiology and risk factors

• The increased susceptibility results from urinary stasis due to hormone-mediated ureteral dilatation and hypoperistalsis and pressure of the enlarging uterus on the ureters.
• The commonest organism is Escherichia coli, which is found in 65–84% of pregnant women with asymptomatic bacteriuria.

Clinical features

Clinical features and complications

• Cystitis presents, as outside pregnancy, with frequency, urgency, dysuria and sometimes nocturia; however, some of these symptoms also occur in pregnancy without infection.
• Acute pyelonephritis occurs mainly in the second and third trimesters and presents with cystitis symptoms, chills, fever, flank pain, colicky abdominal pain, nausea and vomiting; costovertebral angle tenderness is usually present on the affected side.
• In pregnancy pyelonephritis can rapidly progress to sepsis, disseminated intravascular coagulation and acute respiratory distress syndrome; asymptomatic bacteriuria, urinary tract infection and pyelonephritis increase the risk of preterm labour and low birth weight.

Diagnosis

• Asymptomatic bacteriuria is detected by urine culture; in symptomatic infection a urine dipstick is followed by urinalysis and urine culture.
• Group B streptococci in a urine culture, at any colony count, indicate heavy vaginal-rectal colonisation.

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Further reading (selection)

1. MSD Manual Professional Edition: Urinary Tract Infection (UTI) in Pregnancy
2. BMJ Open 2019: Asymptomatic bacteriuria in pregnancy – systematic reviews (PMC, open access)
3. BMC Urol 2019: Etiology and prevalence of UTI and asymptomatic bacteriuria in pregnant women in Iran (PMC, open access)

Cross-references