What is the preferred initial imaging modality for evaluating hydronephrosis in pregnancy?

• A. CT urography
• B. MRI
• C. Renal ultrasound
• D. X-ray

Answer: (C)

Hydronephrosis during pregnancy is most safely and effectively evaluated first with renal ultrasound. It uses no ionizing radiation, making it ideal for fetal safety, and is readily available and noninvasive. Ultrasound can detect dilation of the renal pelvis and calyces, assess whether dilation is unilateral or bilateral, and help distinguish physiologic, pregnancy-related changes from true obstruction. Doppler can add information about flow if needed. If ultrasound findings are inconclusive or more detail is required, MRI can be considered because it avoids radiation, whereas CT urography or X-ray involve radiation and are not preferred during pregnancy.