This patient has nonspecific, common symptoms of pregnancy including urinary frequency, nocturia, back pain, and round ligament pain (ie, sharp groin pain). Although her examination is benign and her laboratory results are normal for pregnancy, a renal ultrasound can be performed due to her recurrent nephrolithiasis. The renal ultrasound findings of bilateral kidney enlargement and bilateral dilation of the renal pelvises and proximal ureters are consistent with physiologic hydronephrosis of pregnancy.
During pregnancy, kidney enlargement occurs because there is an increase in maternal blood volume that requires increased renal filtration, resulting in greater renal vasculature and interstitial tissue. Hydronephrosis begins during the first trimester as high progesterone levels cause ureteral dilation and decreased peristalsis. Hydronephrosis becomes more pronounced in the second and third trimesters as uterine enlargement compresses the ureters at the pelvic brim, which results in dilation of the proximal ureters and bilateral hydronephrosis. Right hydronephrosis is often more pronounced due to dextrorotation of the uterus, which causes increased compression of the right ureter. Unlike pathologic hydronephrosis (eg, secondary to obstruction or infection), physiologic hydronephrosis of pregnancy requires no additional management.
