Fetal megacystis^[1] is a rare disease that is identified by an abnormally large or distended bladder.

Megacystis may be associated with Berdon syndrome (MMIH syndrome).^[2]

Fetal megacystis is diagnosed during pregnancy by ultrasound imaging procedures. Since it can be associated with genetic abnormalities, further ultrasounds and tests may be administered during pregnancy. It may also be diagnosed as megalocystis, and/or termed megabladder, which is the same condition.^{[citation needed]}

Megacystis is listed as a rare disease by the Office of Rare Diseases (ORD) of the National Institutes of Health (NIH), which means it affects fewer than 200,000 people within the U.S.^{[citation needed]}

Megacystis can often be treated pharmacologically or with biofeedback to improve bladder functioning, if the child survives past early infancy.^[2]

• Berdon syndrome