Introduction

The development of symptomatic urolithiasis during pregnancy is anxiety provoking for both patients and urologists. Urolithiasis has been reported as the most common nonobstetric reason for admission during pregnancy, occurring at a rate of about 1 in 200–1,500 pregnancies.^1,2 Pregnancy leads to several physiologic changes that affect the urinary system (fig. 1). However, pregnant women are not at an increased risk for stone events compared with the general population.² Symptomatic urolithiasis has been associated with pregnancy complications such as pre-eclampsia, low birth weight, need for C-section, and a 2-fold increase in rate of preterm delivery.^1,2 Due to the complexity and special attention these patients require, a multidisciplinary approach to managing these patients with the involvement of the urologist, obstetrician, radiologist, and a neonatologist is taken. There is continuous progress being made in the management of these patients with the goal of improving outcomes for both mother and baby.

Figure 1. Summary of physiological changes of genitourinary system due to pregnancy.

Diagnosis

Definitively diagnosing urolithiasis in pregnancy remains a challenge as radiation should be avoided and physiological hydronephrosis is present in up to 90% of patients.³ The first line imaging modality when a pregnant patient presents with renal colic is renal ultrasonography, but it carries a specificity of 86% and a sensitivity of only 34%.³ Transvaginal ultrasound can be used to better visualize a distal stone or to establish if the dilatation only extends to the pelvic brim, suggesting physiological hydronephrosis as opposed to dilatation all the way to the bladder. If ultrasound is nondiagnostic, a secondary imaging modality such as low-dose computerized tomography (CT; positive predictive value of 95.8%) or magnetic resonance urography (MRU; positive predictive value of 89%) should be performed prior to surgery.³ It is believed that radiation doses less than 50 mGy are safe and a single low-dose CT scan typically delivers a dose of 4 mGy to the fetus.⁴ Diagnostic imaging is important as studies have shown a negative ureteroscopy rate of up to 20%, which means that without good preoperative diagnostic imaging 1 in 5 patients may undergo an unnecessary procedure.³

Conservative Management

For patients with well controlled symptoms, stones <1 cm, and no concern for infection, observation is the recommended first line therapy (Strong Recommendation; Evidence Strength: B.)⁵ Reported spontaneous stone passage rates are as high as 70–80%, notably higher than the nonpregnant population, although this number may be falsely elevated due to surgeon bias toward conservative management and misdiagnosis.^6,7 Furthermore, 50% of patients who do not pass their stones during pregnancy will go on to pass them during the post-partum period.⁶ Patients who are appropriate for conservative management can be prescribed acetaminophen, Flomax® (tamsulosin), and as-needed narcotics for symptom management. Obstetrician involvement with a shared decision-making approach is encouraged when prescribing medications during pregnancy and devising a treatment plan. Patients who fail to pass their stone within a reasonable amount of time should be offered intervention.⁵

Operative Management

The indications for initial urinary tract decompression via nephrostomy tube or ureteral stent are the same as for the general population and include infection, poor symptom management, or bilateral obstructing stones.⁵ Those with large stones unlikely to pass on their own (>1 cm) also need intervention. Historically, all of these patients then required serial exchanges every 4–6 weeks until delivery as the risk of encrustation is increased in pregnancy and definitive management was not routinely performed. This subjected many patients to a lengthy exposure to the known problems of indwelling ureteral stents or nephrostomy tubes, including pain, risk of dislodgment, and infection. Additionally, the patient was exposed to numerous anesthetics and hospital visits.

Over the past 2 decades, with advancement in endourology technology and increased sophistication of prenatal care and monitoring, traditional thinking has shifted to offering antepartum ureteroscopy for definitive stone treatment in patients who are deemed low risk and in the second or early third trimester (fig. 2). High risk patients who should not be offered ureteroscopy include patients with obstetric complications, transplant kidneys, abnormal anatomy, significant bilateral stone, or extremely large stone burden, and if there are inadequate support staff or resources available. There have been several large meta-analyses showing that the safety and efficacy of ureteroscopy performed in pregnant patients do not differ significantly from the nonpregnant population.³ Patients can be counseled that the only reported risk to their pregnancy is preterm labor, which is very low (0–1%). Additionally, antepartum ureteroscopy has been shown to be more cost-effective and beneficial for patients when compared to serial stent exchanges.⁸ Finally, operative times should be as brief as possible and ureteroscopy should be performed with ultrasonography alone or with low-dose fluoroscopy with the pelvis covered.

Figure 2. Algorithm for management of nephrolithiasis in pregnancy. HASTE, half-Fourier single shot turbo spin-echo.

The AUA guidelines now reflect this, stating that in pregnant patients with ureteral stones, clinicians may offer ureteroscopy to patients who fail observation. (Strong Recommendation; Evidence Strength: Grade C.)⁵ To ensure that surgery is as safe as possible for the woman and her fetus, it is important that procedures are done at an institution where neonatology and obstetrics are available. Fetal heart tones should be evaluated before and after surgery, and some providers may also want to obtain a nonstress test once the pregnancy has reached viability.⁹ It is important to keep in mind that no currently used anesthetic agents have ever been shown to have teratogenic effects in humans.⁹

Shock wave lithotripsy remains contraindicated in pregnancy due to the risks of miscarriage, congenital malformation, intrauterine growth retardation, and placental displacement.³ The success of percutaneous nephrolithotomy in pregnancy is limited to a few case reports at this time. Therefore, it remains contraindicated during pregnancy due to the increased operative and fluoroscopy time, as well as typically prone positioning.³

Conclusion

Pregnant women with symptomatic urolithiasis present a significant challenge to the urologist, requiring a multidisciplinary treatment approach. The conservative management of urolithiasis in pregnancy is the first line recommendation with analgesia and adequate hydration. Intervention, however, will be necessary at times, and when it is, definitive management with antepartum ureteroscopy should be strongly considered in the properly selected patient. If stone treatment is not appropriate, then decompression with nephrostomy tube or ureteral stent and subsequent serial exchanges thereafter may be necessary. Counseling and shared decision-making remain important during this stressful clinical scenario.