How are kidney stones managed in pregnant women?

Management of Kidney Stones During Pregnancy

For pregnant women with kidney stones and well-controlled symptoms, observation is the first-line therapy, as spontaneous passage rates are similar to non-pregnant patients; if conservative management fails, ureteroscopy is the preferred definitive intervention over temporizing measures like stents or nephrostomy tubes. 1

Initial Coordination and Risk Assessment

• All pharmacological and surgical interventions must be coordinated with the patient's obstetrician before proceeding 1
• Stone events during pregnancy carry increased risk of maternal and fetal morbidity, including preterm labor, requiring close monitoring even with conservative management 1, 2
• The most significant risk is induction of preterm labor, which completely resolves once the stone passes or is removed 1

Diagnostic Imaging Approach

• Ultrasound is the primary and gold-standard first-line imaging modality (sensitivity 45%, specificity 94% for ureteral stones and 88% for renal stones) 1, 2, 3
• MRI should be considered as second-line imaging when ultrasound is nondiagnostic and the patient remains severely symptomatic 1, 3
• Low-dose CT is reserved as a last-line option when other modalities fail to provide necessary diagnostic information 1, 3
• Limited intravenous pyelogram (preliminary film plus two post-contrast films at 15 and 60 minutes) may be considered if ultrasound is unrevealing and symptoms are severe 1

Important Imaging Caveats

Physiological hydronephrosis is common after 20 weeks gestation due to uterine compression and hormonal effects on ureteral peristalsis, which can mimic obstructive uropathy 1. Renal pelvis diameter >21 mm on the right or >25 mm on the left suggests pathologic obstruction requiring intervention 1. Resistive index (RI) >0.70 or RI difference >0.04 between kidneys has high specificity (89-92%) for predicting need for intervention 1.

Conservative Management (First-Line)

Observation with symptom control should be offered as initial therapy when symptoms are well-controlled 1

Pain Management Protocol

• NSAIDs (diclofenac, ibuprofen, metamizole) are contraindicated in pregnancy 1
• Opioids (hydromorphine, pentazocine, or tramadol preferred over pethidine) serve as primary analgesics during pregnancy 1
• Adequate hydration, rest, and antiemetics complete the conservative regimen 1

Medical Expulsive Therapy Considerations

• Alpha-blockers for medical expulsive therapy have not been adequately studied in pregnancy and represent off-label use 1
• Patients must be counseled about the lack of safety data before considering MET 1

Observation Timeline

Most clinicians observe for 24-48 hours before proceeding to intervention if conservative management fails 4. Close follow-up is mandatory given the increased maternal and fetal morbidity risk 1.

Surgical Intervention (When Conservative Management Fails)

Emergency Decompression

In cases of obstructive uropathy with infection and/or sepsis, urgent decompression via percutaneous nephrostomy or ureteral stenting is mandatory 1. Urine must be collected for culture before and after decompression, antibiotics started immediately, and definitive stone treatment delayed until sepsis resolves 1.

Definitive Treatment: Ureteroscopy (Preferred)

Ureteroscopy is the preferred definitive intervention for pregnant patients who fail observation 1

Advantages of URS Over Temporizing Measures

• Accomplishes stone clearance in a single procedure, obviating need for prolonged drainage 1
• Multiple studies demonstrate successful outcomes with very low morbidity and no adverse fetal sequelae 1
• Avoids the need for multiple exchanges of stents or tubes, which rapidly encrust during pregnancy 1
• When intracorporeal lithotripsy is needed, holmium laser has minimal tissue penetration, theoretically limiting fetal injury risk 1

Temporizing Measures: Stents and Nephrostomy Tubes

Ureteral stents and percutaneous nephrostomy tubes are alternative options but require frequent exchanges (typically every 6 weeks) due to rapid encrustation 1, 4

Key Limitations

• Both modalities effectively decompress the collecting system and provide symptom relief 1
• However, foreign objects in the collecting system of pregnant women encrust rapidly, necessitating multiple exchanges throughout pregnancy 1
• This approach is often associated with poor patient tolerance 1
• Ureteral stents and nephrostomy are regarded as equally effective for temporary drainage 4
• Typically, these devices remain in place until delivery, with definitive intervention performed postpartum 1

Contraindicated Procedures

Shockwave lithotripsy (SWL) and percutaneous nephrolithotomy (PCNL) are absolutely contraindicated during pregnancy 2. Only 3.94% of surveyed practitioners reported ever performing PCNL during pregnancy, highlighting its exceptional rarity 4.

Clinical Decision Algorithm

1. Coordinate with obstetrician immediately 1
2. Perform ultrasound as first-line imaging 1, 2, 3
3. If symptoms well-controlled → Observe with opioid analgesia, hydration, antiemetics 1
4. If infection/sepsis present → Emergency decompression (stent or PCN) + antibiotics 1
5. If observation fails after 24-48 hours → Proceed to ureteroscopy for definitive treatment 1, 4
6. If URS not feasible → Temporary stent or PCN with planned exchanges every 6 weeks 1, 4

Common Pitfalls to Avoid

• Do not use NSAIDs (ketorolac) for pain control—they are contraindicated 1
• Do not assume all hydronephrosis is pathologic after 20 weeks gestation—use RI measurements and clinical context 1
• Do not place temporizing stents/tubes without counseling about need for frequent exchanges 1
• Do not delay emergency decompression when infection is present 1
• Do not routinely use CT imaging when ultrasound and MRI remain viable options 1, 3