Daytime Bladder Control Status in Toddlerhood Is Associated With Subsequent Bedwetting in Preschool Years: A Nationwide Cohort Study of Over 30 000 Japanese Children

Objectives: Nocturnal enuresis is common in early childhood. While daytime bladder control typically precedes nighttime continence, the temporal relationship between early daytime bladder control and subsequent bedwetting remains unclear. We investigated whether daytime bladder control status at age 2.5 years—as indicated by diaper use—is associated with bedwetting at age 4.5 years in a Japanese nationwide cohort. Methods: We analyzed data from the Japanese Longitudinal Survey of Newborns in the 21st Century (2010 cohort). Daytime bladder control was assessed at age 2.5 years through caregiver-reported diaper use, and bedwetting frequency at age 4.5 years through parental questionnaires. Modified Poisson regression estimated risk ratios (RRs), adjusting for birth-related factors, socioeconomic status, daycare attendance, and developmental milestones. Results: Among 32 168 children, 26 651 (82.8%) still used diapers at 2.5 years. Bedwetting prevalence at 4.5 years was 42.2%: 34.5% in children who achieved daytime bladder control at 2.5 years versus 43.9% in those still using diapers. After multivariable adjustment, incomplete daytime bladder control at 2.5 years was associated with higher bedwetting risk (adjusted RR 1.25; 95% CI, 1.20–1.31). Multinomial regression revealed dose–response relationships: odds ratios 1.41 (95% CI, 1.30–1.52) for “sometimes” and 1.58 (95% CI, 1.42–1.77) for “often” bedwetting. Conclusions: Daytime bladder control status at 2.5 years was associated with a 25% increased bedwetting risk at 4.5 years. This association likely reflects individual differences in bladder control maturation rather than causal effects. While daytime bladder control may serve as a developmental marker, its validity as an intervention target remains unestablished.