The urinary system consists of the kidneys, the bladder and ureters. The kidneys filter the blood to remove waste products and form urine. The urine passes along the ureters to the bladder, which is held closed by a ring of muscle (sphincter) at the junction of the bladder and the urethra.
When peeing, the muscles of the bladder wall squeeze the urine out of the bladder, at the same time as the muscles in the sphincter need to relax to let the urine flow down the urethra.
The valves between the ureters and bladder prevent urine flowing backwards into the ureters, so that all the urine in the bladder is passed in one go, as the urine cannot travel anywhere else. As the urine leaves the bladder at a high pressure, the valves stop this high pressure being passed on to the kidneys.
A malformed bladder occurs when the baby’s urinary system does not develop correctly. while they are in the womb. So, instead of the tissues and organs forming sealed compartments, the bladder (or the lining of the bladder) may be incomplete, or the link between the bladder, ureter or urethra may be broken.
A malformed bladder rarely occurs in isolation – a child often has other problems with their urinary system, or the bladder abnormality may itself be a symptom of spina bifida (where a baby’s spinal cord and the bones that surround it have not formed properly).
It is not known exactly what causes these abnormalities. There may be a genetic link but research is ongoing – for example, bladder exstrophy affects two to three times more boys than girls and people born with bladder exstrophy have a one in 70 chance of themselves giving birth to a baby with bladder exstrophy.