THE PATIENT is a 34-year-old woman who is 27 weeks pregnant with her second baby. At 12 weeks into her pregnancy, she was found to have an obstructing right renal stone and had a stent placed. At 17 weeks, she was admitted with acute colic and was found to have an obstructed, encrusted stent, which was removed cystoscopically. A nephrostomy tube was placed. She has undergone nephrostomy tube changes but requires them nearly every 2 weeks because of acute encrustation, even using 14F tubes. Now she has persistent bacteriuria, and her gynecologist is concerned she may go into premature labor because of the frequent manipulations required to keep her nephrostomy tube draining. The site has been relocated from a middle to a lower calix to improve pain control and drainage. It is likely she will require some definitive procedure prior to the safer, 32-week time. At 27 weeks, she is high risk regardless of the approach taken. Ultrasound scanning shows a 2.03 2.0-cm renal pelvis stone and numerous stone fragments in the upper pole and on the nephrostomy tube, none larger than 8 mm. There is minimal hydronephrosis and a normal ureter. No radiographs are available to you at this time.