Kidney stones are small, hard deposits of mineral and salt that form inside the kidneys. Although relatively uncommon (occurring in an estimated 1 in 250 to 1,500 pregnancies), they are the most frequent non-obstetric cause of hospitalization for pregnant individuals. Managing a stone requires specialized care that prioritizes the health of both the mother and the developing fetus. Fortunately, safe diagnostic and treatment strategies exist to manage this condition effectively while minimizing risk.
Physiological Changes That Increase Risk and Symptoms
Pregnancy naturally alters the body’s chemistry and anatomy, increasing the likelihood of stone formation. Hormonal shifts, particularly high levels of progesterone, cause the ureters—the tubes connecting the kidneys to the bladder—to relax and dilate. This relaxation, combined with physical compression from the growing uterus, leads to urinary stasis.
This slowed flow allows more time for minerals to crystallize and form stones, especially in the second and third trimesters when the risk of a symptomatic stone increases. Although the body increases levels of stone-inhibiting substances like citrate, the balance often favors the formation of calcium phosphate stones.
Symptoms can be intense, including sharp, wave-like pain often radiating from the flank or back toward the lower abdomen. Blood in the urine, nausea, and vomiting are frequent signs. It is often challenging to distinguish kidney stone pain from other pregnancy-related discomforts, such as round ligament pain or preterm labor contractions.
Safe Diagnostic Procedures During Pregnancy
Diagnosing a kidney stone requires confirming the obstruction without exposing the fetus to unnecessary radiation. Renal ultrasound is the preferred first-line imaging modality. Ultrasound can visualize stones and detect hydronephrosis, which is the swelling of the kidney due to a urine blockage.
A challenge is that physiological hydronephrosis—a normal dilation caused by hormonal changes—occurs in up to 90% of pregnancies, often mimicking a true obstruction. If the ultrasound is inconclusive but symptoms suggest a stone, Magnetic Resonance Imaging (MRI) may be used as a second-line option. MRI provides detailed soft tissue images without using ionizing radiation.
In severe cases where the diagnosis remains uncertain and the mother’s health is compromised, limited exposure to ionizing radiation may be necessary. Low-dose protocols, such as a limited Intravenous Pyelogram (IVP) or a specialized non-contrast Computed Tomography (CT) scan, are reserved for complicated cases. These studies deliver a fetal dose significantly lower than the risk threshold and are coordinated closely with the obstetrician to ensure safety.
Treatment Options Focused on Maternal and Fetal Safety
The treatment approach is primarily conservative unless there is severe obstruction, uncontrollable pain, or a complicating infection. Initial management focuses on observation, aggressive hydration, and safe pain control.
For pain management, opioids are the primary choice, as non-steroidal anti-inflammatory drugs (NSAIDs) are avoided, especially in the third trimester, due to potential effects on fetal circulation. If a urinary tract infection is present, immediate treatment with pregnancy-safe antibiotics is mandatory to prevent a serious kidney infection, which can pose a significant risk for preterm labor.
When conservative management fails, an interventional procedure is required to decompress the kidney and restore urine flow. This is typically achieved by placing a ureteral stent to bypass the obstruction, or a percutaneous nephrostomy tube, which drains urine directly from the kidney through the back.
Ureteroscopy, an endoscopic procedure using a small scope passed through the urethra, is often the preferred definitive treatment for stone removal during pregnancy. This procedure can safely remove the stone in one session. Shock wave lithotripsy (SWL) is contraindicated because the external shock waves could harm the fetus.
The optimal time for an elective interventional procedure, like ureteroscopy, is generally the second trimester. This timing avoids the period of organ development in the first trimester and the challenges of the large uterus in the third trimester. Management is always a collaborative effort involving the urologist and the obstetrics team.
Managing Recovery and Preventing Future Stones
Following the passage or removal of a kidney stone, careful recovery and preventative steps are necessary during the remainder of the pregnancy and in the postpartum period. If a stone was passed or removed, it should be analyzed to determine its specific composition for targeted prevention strategies. Specialized 24-hour urine metabolic studies used to guide prevention are typically postponed until several months after delivery, as pregnancy changes would skew the results.
Preventative measures center on maximizing fluid intake to keep the urine dilute, which is particularly important during the remaining pregnancy. Patients are advised to drink enough water to produce at least two liters of urine daily. Increasing the intake of citrate, found in lemons and limes, can also help inhibit stone formation.
Dietary modifications are tailored to the presumed or known stone type. General guidance includes moderating the intake of high-oxalate foods, such as spinach, nuts, and chocolate. Limiting excessive sodium and animal protein intake is also recommended, as these can increase the risk of stone formation. Follow-up with a urologist postpartum is important for long-term health and to create a comprehensive plan to prevent future recurrences.