In a pregnant patient with suspected nephrolithiasis, which imaging modality is preferred?

• A. Plain X-ray
• B. Ultrasound
• C. Noncontrast CT
• D. MRI

Answer: (B)

In pregnancy, the first and best imaging choice is ultrasound because it avoids exposing the fetus to ionizing radiation while still providing useful information about obstruction. Ultrasound can detect hydronephrosis, which often results from a stone blocking the urinary tract, and it can be performed quickly at the bedside without contrast. This makes it safe across all trimesters and suitable for repeated use as needed during evaluation and management.

Keep in mind that ultrasound may miss some small or distal ureteral stones, and some hydronephrosis can be physiologic in pregnancy due to hormonal and mechanical factors. If ultrasound is nondiagnostic but clinical suspicion remains high, further imaging can be considered. Noncontrast CT is highly sensitive for stones but involves radiation, so it is generally avoided in pregnancy unless absolutely necessary. MRI without contrast is another option when ultrasound is inconclusive and you need additional information, though it is not primarily used to detect stones. Plain X-ray also uses radiation and has limited sensitivity for many stones, so it is not preferred in this setting.