UTI in Pregnancy

Summary

UTIs in pregnancy range from asymptomatic bacteriuria to acute cystitis and pyelonephritis, all of which require prompt recognition and treatment to prevent maternal and fetal complications. Routine screening for ASB in early pregnancy, judicious selection of safe antimicrobials, and close follow-up are essential components of management.

Introduction

Urinary tract infections (UTIs) are among the most common medical complications of pregnancy and are classified into asymptomatic bacteriuria (ASB), lower urinary tract infection (acute cystitis), and upper urinary tract infection (pyelonephritis). All bacteriuria in pregnancy warrants treatment, as untreated infections increase the risk of maternal morbidity, pyelonephritis, and adverse pregnancy outcomes such as preterm labor, intrauterine growth restriction, and low birth weight.

Pathophysiology

Pregnancy predisposes women to recurrent bacteriuria and UTIs due to several physiologic changes:

• Progesterone-mediated smooth muscle relaxation → urinary stasis, ureteral dilation, and vesicoureteral reflux.

• Gravid uterus compression → bladder pressure and ureteral obstruction.

• Relative immunosuppression.
  These changes facilitate bacterial ascension from the lower to the upper urinary tract.
  

Asymptomatic Bacteriuria (ASB)

• Epidemiology: Occurs in 5–10% of pregnancies; most commonly caused by Escherichia coli (≈80%).
  
  

• Risk factors: 

• Urinary stasis.

• Glucosuria.

• Alkaline urine in pregnancy.
  
  

• Diagnosis: Defined as ≥100,000 CFU/mL on urine culture without urinary symptoms. Universal screening is recommended at the first prenatal visit.
  
  

• Complications if untreated: Progression to cystitis (30–40%), pyelonephritis (up to 35%), pregnancy-induced hypertension, preterm labor, intrauterine growth restriction, and low birth weight.
  
  

• Treatment: 

• A 5–7-day course of antibiotics such as cephalexin, nitrofurantoin (avoid near term), oral cephalosporins, or amoxicillin/clavulanate. 

• Fosfomycin may be considered as a single dose. 

• Trimethoprim-sulfamethoxazole (TMP-SMX) may be used with caution (avoid 1st trimester and after 32 weeks). 

• Fluoroquinolones and aminoglycosides should be avoided. 

• A follow-up urine culture is recommended 1 week post-therapy.

Acute Cystitis

• Epidemiology: Occurs in ~1% of pregnancies.
  
  

• Clinical features: 

• Dysuria, urinary frequency, urgency.

• Suprapubic pain without systemic symptoms.
  
  

• Diagnosis: Confirmed by urine culture ≥100,000 CFU/mL in a symptomatic patient.
  
  

• Treatment: 

• Same antibiotic regimens as for ASB, generally for 5–7 days. 

• Empiric therapy should avoid ampicillin or amoxicillin alone due to high E. coli resistance rates. 

• Repeat urine culture may be considered after completion of therapy, especially in recurrent cases.

Pyelonephritis

• Epidemiology: Affects 1–2% of pregnancies, more often primigravidas and more common on the right side.

• Risk factors: 

• Untreated ASB.

• Progression from cystitis.

• Ureteral obstruction, or instrumentation during labor.

• Clinical features: 

• Fever ≥38°C.

• Flank pain.

• Costovertebral angle tenderness.

• Malaise, chills, 

• Nausea.

• Dehydration.

• Systemic toxicity. 

• Up to 20% of cases are associated with uterine contractions and preterm labor.

• Diagnosis: Clinical suspicion supported by positive urine culture and systemic symptoms.

• Treatment: 

• All cases require hospitalization. 

• Management includes: 

• Aggressive IV fluids.

• Monitoring of renal function and electrolytes, and continuous fetal assessment. 

• Empiric parenteral antibiotics (e.g., cephalosporins, aminoglycosides with caution, or ampicillin plus gentamicin) should be administered and tailored to culture results. IV antibiotics are continued until the patient is afebrile and clinically stable, followed by oral therapy to complete a 14-day course. 

• Suppressive therapy for the remainder of pregnancy may be considered in recurrent cases.