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)