Fetal hydronephrosis

Fetal hydronephrosis is dilatation of the fetal renal collecting system. The term is variably defined and at times can overlap with the term fetal pyelectasis (which usually implies a milder form).

Depending on its definition, the estimated prevalence may range between 1-3% of pregnancies.

Marked hydronephrosis (particularly in the 3rd trimester) can result from a number of pathologies which include

Antenatal ultrasound

In the second trimester, severity of fetal hydronephrosis may be graded as 1-2.

  • mild hydronephrosis: anteroposterior renal pelvic diameter (APRPD) measures ≥5 mm (≥4 mm at 16-20 weeks)
  • moderate/severe hydronephrosis: APRPD measures ≥7 mm or if there is associated calyceal dilatation
  • persistent hydronephrosis: ≥10 mm in the 3rd trimester
Ancillary sonographic features
  • dilatation of the renal calyces
  • dilated ureter if obstruction is distal
  • concurrent oligohydramnios if there is bilateral obstruction (or unilateral obstruction with significantly impaired renal function in the other kidney)

Management will depend on the underlying pathology. The degree of renal pelvic dilatation correlates with the outcome. A renal pelvic anteroposterior diameter (APD) of 9 mm or more, and a pelvic-to-renal APD ratio of 0.45 before 32 weeks of gestation and 0.52 thereafter, are considered to be useful for the detection of a severe outcome postnatally 3.

Share article

Article information

rID: 13786
Tag: cases
Synonyms or Alternate Spellings:
  • Antenatal hydronephrosis
  • Marked fetal renal pelvic dilatation

Support Radiopaedia and see fewer ads

Updating… Please wait.

Alert accept

Error Unable to process the form. Check for errors and try again.

Alert accept Thank you for updating your details.