Primary Nocturnal Enuresis
A child is considered to have primary nocturnal enuresis if they are at least 5 years old, have never been dry at night, and wet the bed at least twice a week.
Bedwetting in children who are old enough to have bladder control is usually the result of a variation in normal bladder neurological development. In bedwetters, the signal to wake when the bladder is full is weak or inoperative and the bladder reflex system allows automatic, involuntary voiding when the bladder fills above a certain level.
Other factors that can contribute to bedwetting are deep sleep, small bladder capacity, insufficient ADH hormone to reduce night-time urine production to enable unbroken sleep, and/or an overactive or 'twitchy' bladder.
In a minority of cases bedwetting is caused by anatomic, urological or neurological defects. If there are any concerns it always pays to check with your doctor.