What is the best diagnostic test for suspected kidney stones in a 24-week intrauterine (intrauterine pregnancy) pregnancy?

From the Guidelines

For a 24-week pregnant woman with suspected kidney stones, the recommended diagnostic test is ultrasound of the kidneys, ureters, and bladder (renal ultrasound). This recommendation is based on the evidence from the American College of Radiology, which suggests that ultrasonography is the imaging tool of choice in pregnant patients with flank pain because it has reasonably good sensitivity for stone detection but does not harm the patient or fetus with ionizing radiation 1. The use of ultrasound as the first-line imaging choice during pregnancy is supported by its ability to effectively detect hydronephrosis, ureteral dilation, and many kidney stones, particularly those causing obstruction.

Key Considerations

• Ultrasonography is preferred over other imaging modalities, such as CT scans, due to its lack of ionizing radiation, which poses no risk to the developing fetus 1.
• If ultrasound results are inconclusive but clinical suspicion remains high, a limited low-dose CT scan with abdominal shielding may be considered as a second-line option, though this carries minimal radiation exposure 1.
• MRI without contrast is another radiation-free alternative if ultrasound is insufficient.
• Laboratory tests, including urinalysis for hematuria and urine culture, should accompany imaging to provide a comprehensive diagnosis.

Diagnostic Approach

• The choice of ultrasound balances diagnostic utility with maternal and fetal safety, as radiation exposure during pregnancy should be minimized, especially during critical developmental periods like the second trimester 1.
• The American College of Radiology recommends ultrasonography as the imaging tool of choice in pregnant patients, with a rating of 8, indicating that it is usually appropriate 1.

From the Research

Diagnostic Tests for Suspected Kidney Stones in Pregnancy

• The recommended first-line diagnostic test for suspected kidney stones in a 24-week intrauterine pregnancy is ultrasound, as it is widely used and considered safe during pregnancy 2, 3, 4, 5.
• Ultrasound is highly sensitive for detecting hydronephrosis, but it may not be able to differentiate between ureteral obstruction secondary to calculi and physiologic hydronephrosis 4.
• If ultrasound results are equivocal, magnetic resonance imaging (MRI) can be considered as a second-line test to establish a diagnosis and differentiate physiologic from pathologic dilatation 4.
• Computed tomography (CT) can also be used as a second-line test, but it involves ionizing radiation and should be used cautiously during pregnancy 2, 4.
• Non-contrast CT is sometimes chosen as a first-line or second-line imaging choice, but its use is not universally recommended due to radiation concerns 2.

Considerations for Diagnostic Tests

• The choice of diagnostic test should be made in consultation with a multidisciplinary team, including urologists, obstetricians, and radiologists 4, 5.
• The risks and benefits of each diagnostic test should be carefully considered, taking into account the potential risks to the mother and fetus 3, 6.
• A locally agreed-upon pathway for managing suspected kidney stone disease in pregnancy can help support improved patient care 5.