The exact cause of most cases of nighttime UI is not known. Though a few cases are caused by structural problems in the urinary tract, most cases probably result from a mix of factors including slower physical development, an overproduction of urine at night, and the inability to recognize bladder filling when asleep. Nighttime UI has also been associated with attention deficit hyperactivity disorder (ADHD), OSA, and anxiety. Children also may inherit genes from one or both parents that make them more likely to have nighttime UI.
                
Slower Physical Development
                
Between the ages of 5 and 10, bedwetting may be the result of a small bladder capacity, long sleeping periods, and underdevelopment of the bodys alarms that signal a full or emptying bladder. This form of UI fades away as the bladder grows and the natural alarms become operational.
                
Overproduction of Urine at Night
                
The body produces antidiuretic hormone (ADH), a natural chemical that slows down the production of urine. More ADH is produced at night so the need to urinate lessens. If the body does not produce enough ADH at night, the production of urine may not slow down, leading to bladder overfilling. If a child does not sense the bladder filling and awaken to urinate, wetting will occur.
                
Structural Problems
                
A small number of UI cases are caused by physical problems in the urinary tract. Rarely, a blocked bladder or urethra may cause the bladder to overfill and leak. Nerve damage associated with the birth defect spina bifida can cause UI. In these cases, UI can appear as a constant dribbling of urine.
                
Attention Deficit Hyperactivity Disorder
                
Children with ADHD are three times more likely to have nighttime UI than children without ADHD.2 The connection between ADHD and bedwetting has not been explained, but some experts theorize that both conditions are related to delays in central nervous system development.
                
Obstructive Sleep Apnea
                
Nighttime UI may be one sign of OSA. Other symptoms of OSA include snoring, mouth breathing, frequent ear and sinus infections, sore throat, choking, and daytime drowsiness. Experts believe that when the airway in people with OSA closes, a chemical may be released in the body that increases water production and inhibits the systems that regulate fluid volume. Successful treatment of OSA often resolves the associated nighttime UI.
                
Anxiety
                
Anxiety-causing events that occur between 2 and 4 years of agebefore total bladder control is achievedmight lead to primary enuresis. Anxiety experienced after age 4 might lead to secondary enuresis in children who have been dry for at least 6 months. Events that cause anxiety in children include physical or sexual abuse; unfamiliar social situations, such as moving or starting at a new school; and major family events such as the birth of a sibling, a death, or divorce.
                
UI itself is an anxiety-causing event. Strong bladder contractions resulting in daytime leakage can cause embarrassment and anxiety that lead to nighttime wetting.
                
Genetics
                
Certain genes have been found to contribute to UI. Children have a 30 percent chance of having nighttime UI if one parent was affected as a child. If both parents were affected, there is a 70 percent chance of bedwetting.1