Will a 35 year old female with a history of passing two kidney stones in the last 10 years be at increased risk of stone formation during pregnancy?

Risk of Kidney Stone Formation During Pregnancy

The risk of kidney stone formation is increased during pregnancy, particularly in the second and third trimesters, and peaks in the immediate postpartum period (0-3 months after delivery). 1

Pregnancy-Related Risk Factors for Stone Formation

Pregnancy creates several physiological changes that contribute to increased stone risk:

• Timing of increased risk:

  • Risk begins to increase during the second trimester (OR 2.00) 1
  • Further increases during the third trimester (OR 2.69) 1
  • Peaks at 0-3 months after delivery (OR 3.53) 1
  • Returns to baseline by 1 year after delivery 1

• Physiological changes promoting stone formation:

  • Hypercalciuria: Urinary calcium excretion increases 1-2 fold during pregnancy 2
  • Physiologic hydronephrosis due to ureteral compression by the enlarging uterus 3
  • Urinary stasis from mechanical compression 3
  • Relative dehydration 3
  • Increased risk of urinary tract infections 3

Protective Mechanisms

Despite these risk factors, it's important to note that some protective mechanisms exist:

• Increased urinary thiosulfate levels during pregnancy (approximately 36-40 μM/24 hour across trimesters) may help protect against stone formation despite hypercalciuria 2
• These protective thiosulfate levels return to normal after delivery, along with calcium levels 2

Management Recommendations for Women with History of Kidney Stones

For a woman with a history of kidney stones planning pregnancy, the American Urological Association recommends:

1. Maintain adequate hydration:

   • Increase fluid intake to achieve urine volume of at least 2.5 liters daily 4, 5

2. Dietary modifications:

   • Maintain normal dietary calcium intake (1,000-1,200 mg/day) 4, 5
   • Limit sodium to 100 mEq (2,300 mg) daily to reduce urinary calcium excretion 4, 5
   • If there's a history of calcium oxalate stones with hyperoxaluria, limit intake of oxalate-rich foods 4, 5

Monitoring and Management During Pregnancy

If stone symptoms develop during pregnancy:

• First-line imaging: Renal ultrasonography with color Doppler is recommended 5
• Conservative management: Hydration and appropriate pain control is first-line approach 5
• Regular monitoring: Ultrasound monitoring every 2-4 weeks to assess hydronephrosis 5
• Intervention indications: Failed conservative management, severe infection/pyonephrosis, or solitary kidney with significant obstruction 5

Caution and Considerations

• NSAIDs are contraindicated for pain management during pregnancy 5
• Stone events during pregnancy increase risk of maternal and fetal morbidity, including premature labor 5
• Coordination with an obstetrician is essential for any interventional management 5

For this 35-year-old woman with a history of two kidney stones planning pregnancy, her risk of stone formation will be increased during pregnancy, particularly in the later trimesters and immediate postpartum period. Preventive measures should be implemented before conception and maintained throughout pregnancy.