How is nephrolithiasis (kidney stones) managed in pregnant women?

Management of Nephrolithiasis in Pregnancy

In pregnant patients with kidney stones and well-controlled symptoms, observation should be offered as first-line therapy, with ureteroscopy (URS) as the preferred intervention if conservative management fails. 1

Diagnosis and Initial Assessment

• First-line imaging: Renal ultrasonography with color Doppler is recommended to evaluate for hydronephrosis and rule out obstructive uropathy 2
• Diagnostic indicators on ultrasound:
  • Renal pelvis anteroposterior diameter >16.5 mm in first two trimesters
  • Resistive index (RI) of the kidney >0.70
  • Difference in RI between affected and normal kidneys >0.04 2
• If ultrasound is inconclusive, consider low-dose CT in second and third trimesters 2

Management Algorithm

1. Conservative Management (First-Line)

• Spontaneous passage rates in pregnant women are similar to non-pregnant patients 1
• Key components:
  • Increased fluid intake to achieve urine output >2L/day
  • Appropriate pain control (avoiding NSAIDs which are contraindicated in pregnancy)
  • Regular ultrasound monitoring every 2-4 weeks to assess hydronephrosis progression 2
  • Obtain urine culture if infection is suspected 2

2. Indications for Intervention

• Failed conservative management (persistent symptoms)
• Severe infection/pyonephrosis
• Solitary kidney with significant obstruction 2

3. Interventional Options (When Conservative Management Fails)

A. Ureteroscopy (Preferred)

• Provides definitive treatment by accomplishing stone clearance
• Avoids need for prolonged drainage with stent or nephrostomy tube 1

B. Ureteral Stent Placement

• Effective for decompressing obstructed collecting system
• Drawback: Requires frequent stent exchanges due to rapid encrustation during pregnancy 1

C. Percutaneous Nephrostomy (PCN)

• Indicated if retrograde stenting fails
• Necessary in cases of severe infection/pyonephrosis requiring immediate drainage
• Also used when retrograde stenting is technically not possible 2

Important Considerations

• Multidisciplinary approach: Coordinate pharmacological and surgical intervention with the obstetrician 1
• Monitoring: Stone events in pregnancy carry increased risk of maternal and fetal morbidity, including potential for premature labor 2
• Follow-up: Patients managed conservatively should be followed closely for recurrent or persistent symptoms 1

Prevention Strategies

• Fluid intake: Maintain high fluid intake to achieve at least 2L of urine per day 1
• Dietary calcium: Maintain normal dietary calcium intake (1,000-1,200 mg/day) 2
• Sodium restriction: Limit sodium to 2,300 mg daily to reduce urinary calcium excretion 2
• Oxalate restriction: Consider limiting intake of oxalate-rich foods if there's a history of hyperoxaluria 2

Pitfalls and Caveats

• NSAIDs (including ketorolac) are contraindicated in pregnancy 1
• Foreign objects in the collecting system (stents/tubes) tend to encrust rapidly during pregnancy, necessitating frequent exchanges 1
• Radiation exposure should be minimized; when imaging beyond ultrasound is needed, use the lowest possible dose 2
• Medical expulsive therapy (MET) has not been adequately investigated in pregnant population and would be considered "off-label" use 1