Nephrolithiasis affects up to 7.1% of women, with an increasing prevalence.¹ Among pregnant women, the reported prevalence is 0.14%-0.8% of all deliveries, with hospitalization required among 0.03%-0.4%.² However, the consequences of an acute stone during pregnancy are significant and impact both maternal and fetal health.

Most stone episodes and admissions occur during the second and third trimesters. Presenting symptoms in pregnant patients are similar to those in nonpregnant individuals and include flank pain and hematuria as well as nausea or fevers. Nearly 25% of patients with renal colic during pregnancy are diagnosed clinically without confirmatory imaging.² Misdiagnosis can occur in up to 28% of pregnant women.³

Ultrasonography (US) remains the first-line imaging modality for pregnant women with suspected nephrolithiasis. Reported sensitivities range from 29%-95%.² Based on ureteroscopy as the gold standard, it has a positive predictive value of 77% and false-positive rate of 14%, though false-negative rates have been reported as high as 68%.^2,3 Indirect indicators of an obstructing stone, such as hydronephrosis, may be seen even if a stone is not visualized; this must be differentiated from the physiologic hydronephrosis of pregnancy, which typically does not extend distal to the iliac vessels. Additional imaging features such as greater resistance indices and the absence of ureteral jets may help to differentiate between the two.² Transvaginal ultrasound may also be an useful diagnostic adjunct, particularly for distal ureteral stones.

Magnetic resonance imaging (MRI) and magnetic resonance urography (MRU) is an alternative imaging modality that is currently recommended as second-line imaging for pregnant patients.^4,5 Gadolinium may be used, but static-fluid T2-weighted imaging is typically sufficient for diagnosis; stones appear as signal voids on this phase (Figure 1). Additional signs such as perinephric fluid or the “double kink” sign at the pelvic brim are also suggestive of obstructing ureteral stones. However, despite an 80% positive predictive value, cost, time, and availability may limit its use.

Due to the teratogenic effects of fetal radiation exposure, computed tomography (CT) imaging is generally not recommended for the diagnosis of suspected nephrolithiasis in pregnant women, unless US or MRI are unavailable or inconclusive. However, if necessary, CT may still be obtained in pregnant women, as the typical radiation dose from a single study generally lies below the radiation thresholds associated with fetal harm.⁶ Teratogenic risks are highest during the first trimester, but there are no reported cases of abortion, fetal anomalies, or growth restrictions at exposures <50 mSv.⁶ Where available, low-dose and ultra low-dose techniques can achieve exposures of <4 mSv and even <1 mSv, respectively.⁴

Management of renal colic in the pregnant patient must balance risks and benefits to both mother and fetus, as it is associated with a higher risk of preterm, premature rupture of membranes, low birth weight, preeclampsia, preterm delivery, and infant death.² A multidisciplinary approach is recommended. Most noninfected stones are managed expectantly with hydration, antiemetics, and analgesia, and most patients ultimately pass their stones.³ Nonsteroidal anti-inflammatories and codeine should be avoided during pregnancy due to teratogenic effects, as well as antibiotics such as aminoglycosides, tetracycline, chloramphenicol, fluoroquinolones, and sulfa antibiotics. Tamsulosin is a “category B” medication for use in pregnancy, but is generally considered safe.⁷

Despite this, as many as 26%-30% of pregnant patients with symptomatic nephrolithiasis proceed to intervention.² Indications for treatment are similar to the general population (intractable pain, infection, obstruction in solitary kidney), but also scenarios unique to pregnancy such as preeclampsia or increasing risk of preterm labor.

Percutaneous nephrostomy (PCN) tube placement is a mainstay temporizing therapy for pregnant patients with an obstructing stone. This can be done under ultrasound guidance with minimal anesthesia. Nephrostomy tubes should be exchanged every 4-6 weeks, as they are highly susceptible to encrustation and occlusion in pregnant patients. Most patients require an average of 1-3 PCN exchanges.⁸

Placement of a ureteral stent is an acceptable alternative to PCN. This often involves higher fluoroscopy exposures and anesthesia requirements, though stent placement under US guidance, as well as under spinal or monitored anesthesia, has been described.² Expertise in these areas varies widely between institutions. Stents are poorly tolerated among pregnant patients, and nearly half of women who are stented during pregnancy ultimately undergo early induction due to poor pain control.² Similar to PCNs, ureteral stents require frequent exchanges at least every 4-6 weeks to avoid encrustation and obstruction. Up to 40% of pregnant patients undergo multiple stent exchanges during their pregnancy.⁹

There has been a recent shift towards primary treatment with ureteroscopy in pregnant patients with an obstructing stone. This greatly reduces the number of procedures a patient undergoes per stone episode. The second trimester is the optimal time for ureteroscopy.⁶ Surgery during the first trimester increases risk of abnormal fetal development, while procedures during the third trimester confer increased risk of preterm labor. Ureteroscopy is typically performed under general anesthesia but can be completed using spinal or local anesthesia. Ideally, surgery is performed with as little fluoroscopy as possible. Suggested strategies include selective use of fluoroscopy only during critical steps of the surgery, low-dose and pulsed settings, collimation, and pelvic shielding with a lead apron.² Outcomes for ureteroscopy in pregnant patients are generally thought to be consistent with the general population, and rates of postoperative UTI and ureteral injury rates are similar.¹⁰

Shock wave lithotripsy is not recommended in the pregnant population. Cases of shock wave lithotripsy during pregnancy are associated with increased risk of miscarriage, congenital malformations, intrauterine growth restriction, placental disruption, and fetal death.² Percutaneous nephrolithotomy is also contraindicated during pregnancy.

The management of nephrolithiasis in pregnancy is complex, necessitating shared decision-making between the patient and a multidisciplinary team of urologists, obstetricians, radiologists, and anesthesiologists. Based on the current literature, a proposed management algorithm for the management of renal colic in the pregnant patient is outlined in Figure 2. Though management must be individualized for the specific patient scenario, institutional evidence-based protocols may help facilitate care for pregnant patients with suspected nephrolithiasis.