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Urinary Tract Infection (UTI) in Pregnancy

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1. Why Pregnancy Predisposes to UTI (Effect of Pregnancy on the Disease)

• Ureteral dilation and hydronephrosis: Progesterone-mediated smooth muscle relaxation causes dilation of the calyces, pelves, and ureters - especially on the right side - creating urinary stasis. This allows bacteria already in the lower tract to ascend.
• Decreased ureteral peristalsis: Also progesterone-mediated; reduces clearance of organisms.
• Bladder compression and incomplete emptying: The enlarging uterus compresses the bladder and increases post-void residual volume, allowing bacterial multiplication.
• Glucosuria and aminoaciduria: Normal physiological changes of pregnancy enrich the urine as a bacterial growth medium.
• Relative immunosuppression: The maternal immune system is modified to tolerate the fetal allograft; this may impair uroepithelial defenses.
• Short female urethra: Already a structural risk, compounded by periurethral contamination from vaginal and rectal flora.
• Vesicoureteric reflux: More common in pregnancy, facilitating upper tract involvement.

• Creasy & Resnik's Maternal-Fetal Medicine, p. 1122
• Comprehensive Clinical Nephrology 7e, p. 624

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2. Causative Organisms

• Comprehensive Clinical Nephrology 7e (Box 44.1)

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3. Clinical Features

A. Asymptomatic Bacteriuria (ASB)

• Defined as ≥10⁵ CFU/mL of a uropathogen in a midstream clean-catch urine specimen, in the absence of UTI symptoms
• Prevalence: 2-7% of pregnant women (similar to non-pregnant women of the same age)
• Entirely asymptomatic by definition - no dysuria, frequency, or fever
• Pyuria is present in only 50% of bacteriuric pregnant women, so it is unreliable for screening

B. Acute Cystitis (Lower UTI)

• Dysuria, urinary frequency, urgency, suprapubic discomfort
• Cloudy or malodorous urine
• Usually no fever or systemic signs (distinguishes it from pyelonephritis)
• Occurs in approximately 1-2% of pregnancies independently of pre-existing ASB

C. Acute Pyelonephritis (Upper UTI)

• The most serious form; complicates 1-2% of all pregnancies
• Most commonly presents between 20 and 28 weeks' gestation
• Fever (often high-grade, >38.5°C/101°F) with rigors
• Flank/costovertebral angle (CVA) pain and tenderness (typically right-sided due to ureteral dilation)
• Nausea and vomiting
• Lower urinary tract symptoms (dysuria, frequency) - but not always present
• Acute abdominal pain - can mimic appendicitis or labor
• Uterine irritability and contractions may accompany the illness
• Bacteremia is common (15-20%) and usually transient, but can evolve to sepsis
• Severe complications: acute kidney injury (AKI), disseminated intravascular coagulation (DIC), respiratory distress syndrome (ARDS)

Pyelonephritis can present in pregnancy as acute abdominal pain and may be associated with preterm labor, hypothesized to be triggered by proinflammatory cytokines from bacterial endotoxins. - Comprehensive Clinical Nephrology 7e

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4. Detection and Diagnosis

Screening for ASB

• Universal screening at the first prenatal visit (12-16 weeks) is recommended, as ASB acquired early may persist throughout pregnancy.
• Urine culture is the gold standard - dipstick urinalysis alone is insufficient because pyuria is unreliable (present in only 50% of bacteriuric pregnant women).
• Dipstick is very common in normal pregnancy due to contamination from vaginal secretions - hence culture is preferred over dipstick for primary screening.
• Criteria: ≥10⁵ CFU/mL in a midstream clean-catch specimen; two consecutive specimens recommended in women (a single specimen suffices in men).
• Most maternity units screen at least once; some screen at each trimester.

Diagnosis of Symptomatic UTI

• Urinalysis: Pyuria (>10 WBC/hpf), bacteriuria, nitrites, leukocyte esterase; hematuria may be present
• Urine culture and sensitivity (mandatory before treatment in pregnancy to guide antibiotic choice and detect resistance)
• For pyelonephritis: Blood cultures (bacteremia in 15-20%), CBC (leukocytosis), serum creatinine, electrolytes, LFTs, coagulation screen
• Renal ultrasound: Indicated if no response to treatment within 48-72 hours, to exclude obstruction, pyonephrosis, or perinephric abscess
• Diagnosis of pyelonephritis is primarily clinical; treatment should not be delayed awaiting culture results.

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5. Impact of UTI on Pregnancy Complications

Maternal Complications

Fetal/Obstetric Complications

A Cochrane systematic review indicated that treatment of ASB in pregnancy may reduce the incidence of pyelonephritis, low birth weight, and preterm delivery. - Comprehensive Clinical Nephrology 7e, citing Cochrane evidence

Acute pyelonephritis complicates 1-2% of pregnancies. When this occurs at the end of the second trimester or early in the third trimester, preterm labor and delivery may occur. - Brenner & Rector's The Kidney

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6. Management

A. Management of ASB in Pregnancy

• All pregnant women should be screened and treated if ASB is identified - this is a unique recommendation in pregnancy (unlike non-pregnant adults where treatment of ASB is not generally recommended).
• Treatment for 5-7 days is preferred over single-dose (lower cure rates in pregnancy).
• Antibiotic choice guided by culture sensitivities and trimester safety:

• Follow-up urine culture 1-2 weeks after completion of treatment to confirm eradication
• Women with recurrent bacteriuria may require suppressive therapy for the remainder of pregnancy (e.g., nitrofurantoin 50-100 mg at bedtime)

B. Management of Acute Cystitis

• Treat with a 7-day course of an appropriate oral antibiotic (culture-guided)
• Same antibiotic choices as for ASB apply
• Follow-up culture after treatment

C. Management of Acute Pyelonephritis in Pregnancy

• Mild disease (first half of pregnancy, low-grade fever, normal/slightly elevated WBC, no vomiting, no contractions, compliant): may consider outpatient oral therapy after 12-24 hours of hospital observation
• Most patients in the second half of pregnancy should be hospitalized initially due to the association between pyelonephritis and preterm labor
• Indications for hospitalization: high fever, leukocytosis, vomiting, dehydration, sepsis signs, contractions, no response to initial observation

1. Urinalysis and urine culture before antibiotics
2. Blood cultures (bacteremia in 15-20%)
3. CBC, serum creatinine, electrolytes
4. Continuous vital sign monitoring including pulse oximetry (risk of ARDS)
5. IV crystalloid resuscitation - maintain urine output ≥30-50 mL/hour (but balance against pulmonary edema risk)
6. Parenteral antibiotics - initiated empirically:
   • IV cephalosporins (ceftriaxone, cefazolin) - preferred first-line
   • IV ampicillin + gentamicin - effective combination
   • Fluoroquinolones: avoid in pregnancy unless no alternative
7. Chest X-ray and ABG if dyspnea or tachypnea (ARDS)
8. Fetal monitoring for uterine contractions / fetal wellbeing
9. Step-down to oral antibiotics after 12-24 hours if responding well; complete 10-14 days total

• Resistant organism - repeat culture and adjust antibiotics
• Obstruction - renal ultrasound
• Pyonephrosis or perinephric abscess - CT/ultrasound
• Urological intervention (ureteral stenting, nephrostomy) may be required

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Summary Table

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• Creasy & Resnik's Maternal-Fetal Medicine: Principles and Practice, Chapter 48
• Comprehensive Clinical Nephrology 7th Edition, Chapter 44
• Brenner and Rector's The Kidney, Chapter 36
• National Kidney Foundation Primer on Kidney Diseases 8e
• Textbook of Family Medicine 9e

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URINARY TRACT INFECTION IN PREGNANCY

(High-Yield MBBS / University Exam Answer)

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DEFINITION

• Asymptomatic Bacteriuria (ASB) - ≥10⁵ CFU/mL of a single uropathogen in midstream clean-catch urine with NO symptoms
• Acute Cystitis - lower UTI with symptoms
• Acute Pyelonephritis - upper UTI involving renal parenchyma

UTI is the MOST COMMON MEDICAL COMPLICATION of pregnancy, occurring in up to 20% of pregnancies

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INCIDENCE

• ASB: 2-7% of pregnant women
• Acute cystitis: 1-2%
• Acute pyelonephritis: 1-2%
• 30-40% of untreated ASB progresses to pyelonephritis in pregnancy (vs only 1-2% in non-pregnant women)

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CAUSATIVE ORGANISMS

E. coli strains possess fimbriae (pili) that allow adhesion to uroepithelial cells and facilitate ascending infection

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EFFECT OF PREGNANCY ON UTI

Anatomical Changes:

1. Hydronephrosis and hydroureter - especially right side - due to uterine compression and progesterone effect on smooth muscle → urinary stasis
2. Decreased ureteral peristalsis - progesterone-mediated → reduced clearance of organisms
3. Incomplete bladder emptying - enlarged uterus compresses the bladder → increased residual urine → bacterial multiplication
4. Vesicoureteric reflux (VUR) - more common in pregnancy

Biochemical/Physiological Changes:

1. Glucosuria - normal in pregnancy → excellent bacterial growth medium
2. Aminoaciduria - provides nutrients for bacteria
3. Alkaline urine - promotes bacterial growth
4. Relative immunosuppression - to tolerate fetal allograft → impaired uroepithelial defenses

Structural:

1. Short urethra - pre-existing female anatomical risk
2. Periurethral contamination from vaginal and rectal flora

Net result: ASB progresses to pyelonephritis in 30-40% of untreated pregnant women vs only 1-2% in non-pregnant women

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CLINICAL FEATURES

A. Asymptomatic Bacteriuria (ASB)

• No symptoms by definition
• Only detected on routine screening
• Pyuria present in only 50% (therefore pyuria alone is unreliable for screening)

B. Acute Cystitis (Lower UTI)

• Dysuria
• Urinary frequency and urgency
• Suprapubic pain/discomfort
• Cloudy, malodorous urine
• Haematuria (occasionally)
• NO fever (important distinguishing feature from pyelonephritis)
• NO systemic signs

C. Acute Pyelonephritis (Upper UTI)

• Most commonly presents at 20-28 weeks gestation
• Fever - high grade, with rigors/chills
• Costovertebral angle (CVA) tenderness - typically right-sided
• Nausea and vomiting
• Flank pain radiating to the groin
• Lower urinary symptoms (not always present)
• Uterine contractions - preterm labor may occur
• Acute abdominal pain - can mimic appendicitis
• Bacteremia - occurs in 15-20% (usually transient)

Severe/Complicated Pyelonephritis Features:

• High fever (>39°C), rigors
• Septic shock - hypotension, tachycardia
• Dyspnea, tachypnea → ARDS (endotoxin-mediated)
• Oliguria → Acute Kidney Injury (AKI)
• DIC in severe sepsis
• Pyonephrosis/perinephric abscess - if no response to antibiotics

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DETECTION / DIAGNOSIS

Screening Protocol:

• Screen ALL pregnant women for ASB at first prenatal visit (12-16 weeks)
• Urine culture is GOLD STANDARD - NOT dipstick alone
• Dipstick is unreliable because vaginal secretion contamination is common and pyuria is present in only 50% of bacteriuric pregnant women

Diagnostic Criteria for ASB:

• ≥10⁵ CFU/mL of a single uropathogen in midstream clean-catch urine
• Two consecutive specimens required in women (single specimen sufficient in men)

Investigations for Symptomatic UTI:

Note: Treatment should NOT be delayed pending culture results in pyelonephritis

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IMPACT OF UTI ON PREGNANCY COMPLICATIONS

MATERNAL COMPLICATIONS:

FETAL / OBSTETRIC COMPLICATIONS:

Key exam point: Untreated ASB → 30-40% risk of pyelonephritis → preterm labour → major cause of perinatal morbidity/mortality

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MANAGEMENT

ANTIBIOTICS SAFE IN PREGNANCY - SUMMARY TABLE:

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A. MANAGEMENT OF ASB

1. Treat ALL cases in pregnancy (unlike non-pregnant adults)
2. Culture-guided oral antibiotics for 5-7 days
   • Preferred: Nitrofurantoin 100 mg BD, OR Cephalexin 500 mg QID
3. Test of cure: Urine culture 1-2 weeks post-treatment
4. If recurrent: Suppressive therapy for rest of pregnancy
   • Nitrofurantoin 50-100 mg at bedtime

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B. MANAGEMENT OF ACUTE CYSTITIS

1. Oral antibiotics for 7 days (culture-guided)
2. Preferred agents: Cephalexin, Nitrofurantoin, Amoxicillin-clavulanate
3. Avoid: Fluoroquinolones, Tetracyclines, TMP-SMX in 1st trimester
4. Follow-up culture after treatment

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C. MANAGEMENT OF ACUTE PYELONEPHRITIS

Step 1 - Assess Severity and Decide Setting:

Most experts: 12-24 hours initial hospital observation before deciding on outpatient discharge even for mild cases

Step 2 - Hospital Management Protocol:

• Vital signs q4-hourly including pulse oximetry
• Urine output monitoring (target ≥30-50 mL/hour)
• Fetal monitoring for contractions

• Urine C/S before antibiotics
• Blood cultures, CBC, RFTs, electrolytes
• CXR + ABG if dyspnoea (rule out ARDS)

• Aggressive IV crystalloid resuscitation (normal saline/Ringer's lactate)
• Balance against pulmonary oedema risk - close respiratory monitoring

• IV Ceftriaxone 1g OD - PREFERRED FIRST LINE
• IV Cefazolin 1g TID - alternative
• IV Ampicillin + Gentamicin - effective combination
• Step-down to oral antibiotics after 12-24 hours of clinical improvement
• Total duration: 10-14 days

Step 3 - If No Response in 48-72 Hours:

• Repeat urine culture → adjust antibiotics based on sensitivity
• Renal ultrasound → rule out obstruction, pyonephrosis, perinephric abscess
• Urological intervention if needed (ureteral stenting, percutaneous nephrostomy)

Step 4 - Post-treatment:

• Suppressive antibiotics for remainder of pregnancy (Nitrofurantoin 50-100 mg nocte)
• Repeat urine cultures each trimester

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PREVENTION

1. Universal screening for ASB at booking visit
2. Adequate hydration
3. Frequent voiding (avoid urine retention)
4. Voiding after intercourse
5. Perineal hygiene (wipe front to back)
6. Treat ASB promptly to prevent progression
7. Suppressive therapy for recurrent UTI

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EXAM QUICK RECALL POINTS

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