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Fetal megacystis

Fetal megacystis refers to the presence of an unusually large bladder in a fetus. It is generally defined as a 

  • bladder diameter > 7 mm in the first trimester 3
  • bladder diameter > 30 mm in the second trimester reference required
  • bladder diameter > 60 mm in the third trimester reference required


The estimated incidence of antenatal imaging is at ~ 1 : 1500 pregnancies.


It can result from a number of causes but with the main underlying mechanism being either a distal stenosis of reflux.


Associated anomalies are common 6 and include 

Radiographic assessment

Antenatal ultrasound

Will show an enlarged bladder

Ancilliary sonographic findings

Treatment and prognosis

The overall prognosis can be variable from progressive obstruction to spontaneous resolution. A follow-up ultrasound is necessary to correctly interpret the significance of megacystis detected in the first trimester

If the fetus is chromosmally normal and there is megacystis on the 1st trimester scan

  • there is spontaneous resolution of the megacystis in about 90% of cases when the 1st trimester longitudinal bladder diameter is between 7 - 15 mm 4.  
  • if the bladder diameter is > 15 mm there is a very high likelihood  of associated with progressive obstructive uropathy 4

Management will depend on the underlying pathology

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