Increased Risk of Kidney Stone Formation During the Third Trimester and Early Postpartum Period
The third trimester of pregnancy carries the highest risk of kidney stone formation, with the peak risk occurring in the first 0-3 months after delivery. 1
Physiological Changes and Risk by Trimester
First Trimester
- Similar risk to non-pregnant women (OR 0.92) 1
- Minimal physiological changes affecting stone formation
Second Trimester
- Risk begins to increase significantly (OR 2.00) 1
- Physiologic hydronephrosis begins to develop in >80% of pregnant women 2
Third Trimester
- Substantially higher risk (OR 2.69) 1
- Physiologic hydronephrosis reaches maximum
- Increased urinary calcium excretion
Postpartum (0-3 months)
- Peak risk period (OR 3.53) 1
- Risk returns to baseline by 1 year after delivery
Stone Composition During Pregnancy
Unlike the general female population where calcium oxalate stones predominate, pregnant women develop:
- Calcium phosphate (hydroxyapatite) stones in 74% of cases 3
- Calcium oxalate stones in only 26% of cases 3
This unusual predominance of calcium phosphate stones likely reflects the unique physiological changes of pregnancy.
Diagnostic Approach for Suspected Stones
For pregnant women with flank pain and suspected kidney stones:
- Renal ultrasonography with color Doppler is the first-line imaging approach 4, 2
- Evaluate for:
- Anteroposterior diameter of renal pelvis
- Resistive index of the kidney
- Direct visualization of stones
- Ureteral jets 2
- Low-dose CT may be considered in the second and third trimesters if ultrasound is inconclusive 2
Management Considerations
Conservative Management
- First-line approach for uncomplicated stones 2
- Includes:
- Adequate hydration
- Appropriate pain control (avoid NSAIDs)
- Regular ultrasound monitoring every 2-4 weeks 2
Intervention Indications
- Failed conservative management
- Severe infection/pyonephrosis
- Solitary kidney with significant obstruction
Intervention Options
- Ureteroscopy is the preferred interventional approach 2
- Retrograde ureteral stenting if ureteroscopy not feasible 2
- Percutaneous nephrostomy for cases where retrograde stenting fails 2
Prevention Strategies
For women with history of stones planning pregnancy:
- Maintain normal dietary calcium intake (1,000-1,200 mg/day) 2
- Limit sodium to 2,300 mg daily 2
- Increase fluid intake to achieve urine volume of at least 2.5 liters daily 2
- Limit intake of oxalate-rich foods if history of hyperoxaluria 2
Clinical Implications
Understanding the timing of increased stone risk during pregnancy allows for:
- More vigilant monitoring during the third trimester and early postpartum period
- Earlier intervention for symptomatic stones
- Appropriate counseling for women with prior stone history
- Implementation of preventive measures during high-risk periods
The increased risk of kidney stones during late pregnancy and early postpartum represents a significant clinical concern that requires careful monitoring and management to minimize maternal morbidity and potential complications.