Background: Foetal megacystis is the enlargement of the foetal bladder seen on prenatal ultrasound. Diagnosing the underlying cause of foetal megacystis in the antenatal period is often challenging due to the many possible underlying aetiologies, including various obstructive and non-obstructive causes. Summary: The detection of foetal megacystis leads to an extensive diagnostic conundrum. Counselling, prognostication, and prenatal management may prove challenging. Prenatal intervention has been trialled with limited success. Key Messages: This review article aims to be a practical guide to assist with the diagnosis, management and counselling for foetal megacystis in each trimester. It summarizes the evidence for each differential diagnosis and how to distinguish between them.

Megacystis, or an enlarged foetal bladder, is an uncommon but important finding on prenatal ultrasound. Once seen, it is important to determine the underlying aetiology to guide appropriate investigations, management and counselling of the families. This review article aims to demystify megacystis and offers a practical guide for the diagnosis and management of these cases.

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