Prognostic factors of severe foetal megacystis

At antenatal ultrasound, severe megacystis implies high foetal mortality rate. Traditionally, many of these foetuses undergo termination of pregnancy. We undertook a study to investigate the prognostic factor(s) for megacystis foetuses.

61 consecutive cases of antenatally diagnosed severe megacystis between 1988 to 2008 were reviewed from a statewide tertiary referral centre for major foetal abnormalities. The data included the ultrasonic measurements and post-mortem pathologies.

Mean gestational age (GA) at diagnosis was 17.0 weeks (range 11 to 39). The average bladder diameters for GA 10 to 14 weeks, 15 to 26 weeks, and 27 to 39 weeks were 32.5 mm, 45.7 mm, and 57.2 mm respectively. In males the most common cause of megacystis was posterior urethral valves in 32.6% (n = 17). The most common cause in females was urethral stenosis in 33% (n = 3). We compared the relative bladder size (as a percentage of normal for that gestational age) between the survivor group (n = 14) and the foetal/neonatal death group (n = 17). All terminations (n = 20) were excluded. The bladder sizes of the two groups were almost identical (310.2 ± 108% vs. 309.8 ± 120%). We analysed various prognostic factors. Megacystis foetuses with oligohydramnios had an increased risk of death compared to those who had megacystis without oligohydramnios (OR = 6.0; 95% CI 1.26 - 28.5, Chi-square: P = 0.019).

Relative bladder size alone does not predict survival. The combination of severe megacystis and oligohydramnios implies complete obstruction of bladder outlet and is associated with high mortality rate. This provides clinicians with measurable evidence to predict survival. It also gives parents the option of avoiding unnecessary termination of pregnancy.