Variable incidence depending on source – between 1 in 200 and 1 in 1500.
Overall incidence appears similar to non-pregnant women of similar ages.
Most patients present in second and third trimester.
Physiological changes in pregnancy contributing to stone formation:
- Increased vitamin D levels (placental production) -> hypercalciuria
- Increased renal blood and GFR -> increased filtered solute load
- Increased urinary concentration of stone inhibitors (citrate and Mg)
- Increased urinary calcium and glucose
- Increased urine volumes (preventative)
- Stasis and increased renal pelvis pressures due to physiological hydronephrosis
- Elevated urine pH (calcium phosphate stones most common in pregnant women)
Physiological changes leading to hydronephrosis:
- Increased renal blood flow, with GFR increasing by 50 % and increased urine output
- Mechanical compression of pelvis and retroperitoneum causing dilation of collecting systems, right > left
- Higher levels of progesterone causes smooth muscle relaxation
- Right sided more common due to gravid uterus dextro-rotation, left side protected by gas filled sigmoid, and potentially right ureter compressed by dilated right gonadal vein
- Right sided dilation in up to 90 % by end of third trimester
- Historically average 15 mm right sided pelvicalyceal dilation, 5 mm on left
Management principles:
- Multidisciplinary care shared with obstetrician
- Consider alternate diagnoses as causes of pain (appendicitis, pyelonephritis, colitis)
- Observation and conservative management should be first line in the absence of infection and uncontrolled pain
- Attempt to avoid risks to pregnancy – i.e., ionising radiation, risks of anaesthesia, risks of sepsis
- Management should be undertaken in a centre with both urological and obstetric capability
Investigation of women with loin pain:
- History – loin pain, symptoms of infection, history of UTIs, haematuria and urinary symptoms, obstetric history and complicating features
- Examination – vital signs, flank tenderness, health of child
- Blood tests including renal function
- Urine analysis – blood, nitrites, leukocytes
Ultrasound is first line imaging modality
- Operator dependent
- Renal pelvis, proximal ureteric and VUJ stones may be visible; not mid ureteric
- Ureteric jet may be useful
- Resistance index
MRI is second line – indicated if concerns for ureteric stone not elucidated on ultrasound
- No radiation
- Non contrast
- May be difficult to access
- Stones visualised as filling defects in the high intensity signal of urine on T2
CT has best sensitivity and specificity but its use is limited by radiation dose, however:
- Radiation exposure from non contrast CT is much lower than exposure associated with foetal harm
- Radiation doses < 50 mGy considered safe in pregnancy
- Risk minimised in third trimester
- Should be used as last line imaging
Management of symptomatic stones
In the presence of infection -> ureteric stent.
In the presence of symptoms:
- Conservative management preferred in the absence of strong indications for intervention
- Alpha blockers have not been studied in pregnancy
- 70 – 80 % stones can be successfully managed conservatively
- Stent (or nephrostomy) which can be maintained during pregnancy, then proceeding to definitive ureteroscopy after pregnancy
- Primary ureteroscopy and laser of stone
ESWL is contra-indicated.
PCNL has only limited evidence and should rarely be needed in individualised cases in experienced centres.
Nephrostomy is a reasonable alternative to stenting:
- Can be done without GA
- Can be done with radiation under ultrasound, and changed in the same way without GA or ultrasound
Ureteric stents tend to encrust quicker in pregnancy due to hypercalciuria and hyperuricosuria:
- Stents often poorly tolerated with significant analgesia requirements
- Reduced quality of life
- May require frequent changes 4 – 8 weekly (with risks associated each time)
- May be nidus for bacteriuria and subsequent complicated UTIs/sepsis
Principles of operating on pregnant women:
- Defer operating if possible – but – do not withhold necessary surgery just because a woman is pregnant
- Multidisciplinary decision making with obstetricians and anaesthetics
- Consider elevating right side to reduce caval compression which reduces venous return
- Remember significantly higher VTE risk in pregnant women.
- Foetal Doppler/monitoring is usually used pre and post-operatively to exclude complication and reassure mother
- GA can theoretically risk pre-term labour although these risks are small in absolute terms
- Avoid excess stimulation of cervix during prep
- Consider omitting fluoroscopy, using ultrasound to check stent placement if available
- Second trimester is optimal time to operate (avoid risk of inducing labour)
- No anaesthetic agents seem to have teratogenic effects
- Operations should be done at hospitals with appropriate neonatal and obstetric services, and obstetricians should be aware the procedure is happening and available if needed
- Avoid high pressures if operating laparoscopically (aim < 15 mm Hg).
NSAIDs are generally contra-indicated in pregnancy, especially after 20 – 30 weeks.
Penicillins and cephalosporins safe in pregnancy. Gentamicin also commonly used.
Fluoroquinolones contra-indicated. Bactrim/trimethoprim contra-indicated in first trimester (folic acid inhibitor). Nitrofurantoin contra-indicated in third trimester.