Causes of Antenatal Hydronephrosis

The most common cause of antenatal hydronephrosis is a narrowing of the ureter close to the kidney, usually developing before the fourth month of pregnancy.

Other causes include the following:

  • Blockage (in the kidney, at the uteropelvic junction [UPJ]; in the bladder, at the uterovesical junction; or in the urethra, due to the posterior urethral valves)
  • Reflux (condition in which the valve between the bladder and the ureter allows urine to flow back into the kidney when the bladder fills or empties)
  • Duplication anomaly (occurs in 1 percent of the population and involves two ureters leading from the kidney; one may have an obstruction called a uterocele)
  • Multicystic kidney (nonfunctional kidney)

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 09 Jun 1998

Last Modified: 01 Sep 2015