Nephrolithiasis in Pregnancy

Nephrolithiasis in pregnancy is stone formation in the kidney or ureter, presenting with renal colic, usually in the second or third trimester. It matters because it mimics other causes of abdominal pain and, if obstructed and infected, causes sepsis and preterm labour.

• Risk factors: previous stones, hypercalciuria, dehydration, urinary infection, hyperparathyroidism, hot climate.
• Most small stones pass spontaneously.
• Imaging avoids ionising radiation where possible.

Women have sudden severe colicky loin pain radiating to the groin, nausea, vomiting, haematuria and frequency, often with restlessness. Examine temperature, loin tenderness and uterine contractions.

• Haematuria in most.
• Fever suggests infected obstruction.
• Differential diagnosis: pyelonephritis, appendicitis, ectopic pregnancy, ovarian torsion, placental abruption, preterm labour, cholecystitis, physiological hydronephrosis.
• Complications: obstruction, infection, sepsis, acute kidney injury, preterm labour, recurrent colic, loss of kidney function.

The approach is ultrasound first, with magnetic resonance imaging or low dose CT if unclear.

• Renal ultrasound: stone, hydronephrosis (note physiological dilatation of pregnancy), absent ureteric jet, resistive index above 0.7.
• Transvaginal ultrasound to show the distal ureter; MRI urography without gadolinium for uncertain cases; low dose CT as a last resort.
• Urinalysis with microscopy and culture; creatinine, electrolytes, calcium, uric acid, full blood count.
• Stone analysis and metabolic work up after delivery.

The principle is analgesia, hydration and observation for stones below 10 mm, with drainage for infection or obstruction.

• Supportive: oral fluids 3 litres daily or IV Ringer's lactate 1 litre over 4 hours; warm compress; strain urine; left lateral position; hourly output if admitted.
• Pharmacological: paracetamol 1 g oral or IV 6-hourly (maximum 4 g in 24 hours); morphine 2.5 to 5 mg IV 4-hourly as needed; avoid NSAIDs after 20 weeks; ondansetron 4 mg oral or IV 8-hourly for vomiting; ceftriaxone 2 g IV daily for infection followed by cefalexin 500 mg oral 6-hourly to complete 10 to 14 days; potassium citrate and thiazides are avoided in pregnancy; prophylaxis: cefalexin 250 mg oral at night until 6 weeks postpartum if recurrent infection.
• Procedures: ureteric stent or percutaneous nephrostomy for infected obstruction, intractable pain or single kidney, replaced every 4 to 6 weeks because of encrustation; ureteroscopy with laser in the second trimester for persistent stones; shock wave lithotripsy is contraindicated.
• Special groups: hyperparathyroidism needs parathyroidectomy in the second trimester; women with a single kidney or renal impairment need earlier drainage.
• Red flags: fever above 38 degrees Celsius, rigors, anuria, intractable pain, rising creatinine, contractions.
• Follow-up: review at 1 week; repeat ultrasound at 2 to 4 weeks; stone analysis and metabolic work up at 6 weeks postpartum; stent removal after delivery.