Definition of uti in pregnancy Signs and symptoms Management Complications
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"urinary tract infection" AND pregnancy
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Urinary Tract Infection (UTI) in Pregnancy
1. Definition
UTI in pregnancy refers to the presence and multiplication of bacteria anywhere in the urinary tract - from the urethra to the kidneys - during gestation. It encompasses three clinical entities:
A. Asymptomatic Bacteriuria (ASB)
The presence of bacteria in the urine (≥10² CFU/mL in a symptomatic patient; ≥10⁵ CFU/mL on a single midstream clean-catch specimen) without any symptoms of urinary tract infection. Although most women who have ASB in pregnancy actually acquired it before conception, pregnancy dramatically increases the risk of ASB progressing to pyelonephritis (up to 40% if untreated).
B. Acute Cystitis (Lower UTI)
Symptomatic infection confined to the bladder and lower urinary tract.
C. Acute Pyelonephritis (Upper UTI)
Infection involving the renal parenchyma and pelvis - one of the most common serious medical complications of pregnancy, occurring in 1-2.5% of all pregnancies.
2. Why Pregnancy Predisposes to UTI (Pathophysiology)
Multiple physiologic changes in pregnancy facilitate bacterial ascent and replication:
- Progesterone effects: Decreased ureteral muscle tone and peristalsis → urinary stasis → static columns of urine in ureters
- Mechanical obstruction: Enlarging uterus compresses ureters, especially on the right (right-sided hydronephrosis in 75%, left-sided in 33% by mid-pregnancy)
- Bladder changes: Decreased tone, increased capacity, and incomplete emptying → vesicoureteric reflux
- Urinary pH: Increased bicarbonate excretion raises urinary pH → promotes bacterial growth
- Glycosuria: Common in pregnancy; favors bacterial multiplication
- Increased estrogen excretion: Accelerates growth of uropathogenic E. coli
The cumulative result is physiologic hydronephrosis and urinary stasis, creating an environment where bladder infection can easily ascend to the kidneys.
3. Causative Organisms
| Organism | Notes |
|---|---|
| Escherichia coli | >70-85% of all cases; most virulent strains have fimbriae/pili for urothelial adhesion, K antigen, hemolysin |
| Klebsiella spp. | Second most common gram-negative |
| Proteus spp. | Especially in diabetic women or urinary tract obstruction |
| Enterococci | Gram-positive |
| Staphylococcus saprophyticus | Young sexually active women |
| Group B Streptococcus | Important in pregnancy (also neonatal risk) |
| Pseudomonas | Less common; multiresistant strains increasingly seen |
(Source: Comprehensive Clinical Nephrology, 7th Ed., Box 44.1; Creasy & Resnik's MFM)
4. Signs and Symptoms
Asymptomatic Bacteriuria
- No symptoms by definition
- Detected only on routine urine culture screening (recommended at first antenatal visit, ideally 12-16 weeks)
Acute Cystitis (Lower UTI)
- Dysuria (burning/pain on urination)
- Urinary frequency and urgency
- Suprapubic pain/discomfort
- Haematuria (microscopic or visible)
- Cloudy or malodorous urine
- No fever, no systemic features
- Negative urine dipstick does not exclude infection in symptomatic women (false-negative rate significant, especially with gram-positive organisms)
Acute Pyelonephritis (Upper UTI)
- Most commonly presents between 20-28 weeks' gestation
- Fever (often high-grade, with rigors)
- Flank/loin pain (costovertebral angle tenderness), typically right-sided
- Nausea and vomiting
- Malaise and systemic illness
- Lower urinary tract symptoms may or may not precede the upper tract symptoms
- Can present as acute abdominal pain and mimic other surgical conditions
- Signs of preterm labour may be present (due to proinflammatory cytokine release from bacterial endotoxins)
5. Diagnosis
| Investigation | Detail |
|---|---|
| Urine culture (midstream clean-catch) | Gold standard - single positive specimen (≥10⁵ CFU/mL) used in practice; gold standard for ASB screening |
| Urine dipstick | Sensitivity 75%, specificity 82%; positive leukocyte esterase or nitrite = treat; negative does NOT rule out infection |
| Urinalysis/microscopy | Pyuria, bacteriuria; isolated pyuria is common in normal pregnancy due to vaginal contamination |
| Blood cultures | Indicated in pyelonephritis (bacteraemia is a common, often transient complication) |
| Renal ultrasound | For pyelonephritis not responding to treatment; to exclude obstruction, abscess, calculi |
| FBC, U&E, CRP | Baseline in pyelonephritis |
Both the US Preventive Services Task Force and the Infectious Diseases Society of America recommend urine culture (not dipstick alone) as the screening test for ASB in pregnancy.
6. Management
A. Asymptomatic Bacteriuria
- Treat all cases - reduces pyelonephritis, preterm birth, and low birth weight
- A 7-day course is usually recommended (insufficient evidence favoring 3-day or single-dose)
- First-line antibiotics:
- Amoxicillin 500 mg PO 2-3 times daily for 3-7 days
- Cephalexin 500 mg PO 2-4 times daily for 3-7 days
- Perform "test of cure" urine culture after completion of treatment
- Without treatment, ASB persists in 80%; even with treatment, 20% have persistent bacteriuria
B. Acute Cystitis
- Immediate antibiotic therapy (same agents as ASB)
- Duration: 3 days for initial infection; 7-10 days for recurrent
- Single-dose therapy is not recommended in pregnancy
- "Test of cure" culture 1-2 weeks after completing treatment
- For 3+ symptomatic UTIs in 12 months: continuous prophylaxis with nitrofurantoin or TMP-SMX (one tablet daily); postcoital prophylaxis is an alternative
C. Acute Pyelonephritis
- Hospital admission is standard practice (outpatient management acceptable for mild cases)
- IV broad-spectrum antibiotics initially (e.g., cephalosporins, aminoglycosides), then switched based on culture sensitivity
- IV fluids and antipyretics
- Fetal monitoring (risk of preterm labour)
- Prophylactic antibiotics continued until delivery to prevent recurrence
- Renal ultrasound if not responding to treatment
- If persistent despite adequate antibiotics and pathologic ureteric dilation confirmed - percutaneous nephrostomy under ultrasound guidance
Antibiotic Safety in Pregnancy
| Antibiotic | Trimester Safety |
|---|---|
| Amoxicillin / Cephalexin | Safe in all trimesters - first-line |
| Nitrofurantoin | Avoid in 1st trimester (unless no alternative); avoid near term (neonatal haemolysis risk) |
| Trimethoprim | Avoid in 1st trimester (anti-folate; risk of neural tube defects) and avoid with folate deficiency |
| Trimethoprim-sulfamethoxazole | Sulfonamide component: avoid in 3rd trimester (kernicterus risk in neonate) |
| Fluoroquinolones | Contraindicated - cartilage damage in fetus |
| Tetracyclines | Contraindicated - bone/dental effects in fetus |
7. Complications
Maternal Complications
| Complication | Details |
|---|---|
| Acute pyelonephritis | Up to 40% of untreated ASB cases; most serious immediate complication |
| Bacteraemia/Sepsis | Common (often transient) with pyelonephritis; can progress to septic shock |
| Acute Kidney Injury (AKI) | Especially with severe sepsis |
| Disseminated Intravascular Coagulation (DIC) | Rare, with severe sepsis |
| Respiratory distress / ARDS | Rare, severe complication of pyelonephritis-associated sepsis |
| Pyonephrosis / Perinephric abscess | Rare; suspect if no response to antibiotic therapy |
| Recurrent UTI | Recurrence in 10-18% during the same pregnancy; up to 60% without suppressive therapy |
| Anaemia | Haemolytic anaemia has been reported with pyelonephritis |
Fetal/Obstetric Complications
| Complication | Details |
|---|---|
| Preterm labour | Endotoxins stimulate prostaglandin and proinflammatory cytokine release → uterine contractions |
| Preterm birth | Risk increases with untreated ASB and pyelonephritis |
| Low birth weight | Associated with untreated ASB/cystitis |
| Fetal mortality | Rare; associated with severe maternal sepsis |
| Intrauterine growth restriction | Indirect effect via sepsis and inflammatory state |
In the pre-antibiotic era, maternal mortality from pyelonephritis was 3-4%. In high-income countries today, death from pyelonephritis in pregnancy is rare but remains a possibility in severe, complicated cases.
Key Takeaways
- Screen all pregnant women for ASB by urine culture at first antenatal visit - treat every positive culture regardless of symptoms
- E. coli accounts for >70% of UTIs in pregnancy
- Untreated ASB progresses to pyelonephritis in up to 40% of cases
- Fluoroquinolones and tetracyclines are contraindicated; TMP-SMX and nitrofurantoin require trimester-specific caution
- Pyelonephritis is a leading cause of preterm labour and is managed with IV antibiotics and hospital admission
- A "test of cure" culture after treatment is mandatory in pregnancy
Sources: Creasy & Resnik's Maternal-Fetal Medicine, Principles and Practice; Comprehensive Clinical Nephrology, 7th Ed.; Tintinalli's Emergency Medicine; Global prevalence of UTI in pregnant mothers (meta-analysis, 2023) - PMID 37734277
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