Maternal hydronephrosis in pregnancy: poor association with symptoms of flank pain

The purpose of our investigation was to determine the association between flank pain and maternal hydronephrosis during pregnancy. Eighty-one gravidas were evaluated longitudinally with renal ultrasound in each trimester and postpartum. Each was asked about symptoms of flank pain, and then a renal ultrasound was performed. We defined hydronephrosis as a mean pelvic-calyceal measurement of 10 mm or greater. None of the cohort had hydronephrosis in the first trimester, and four had hydronephrosis in the second trimester; almost all maternal hydronephrosis was seen initially in the third trimester. Seventeen (21%) of 81 women had hydronephrosis; 14 on the right side and three bilateral. Nine women reported significant flank pain, and three of these had hydronephrosis. Fourteen women with hydronephrosis reported no flank pain. There was no association observed between flank pain and hydronephrosis ( P = 0.39). All women with hydronephrosis had complete resolution at 6 weeks postpartum. During pregnancy, the association between maternal hydronephrosis and flank pain symptoms is poor. In the clinical evaluation of pregnant women with flank pain, hydronephrosis should not be considered etiologic in the absence of other clinical evidence.