Later Training, More Bladder Problems: A Meta-Analysis (Li, Wen et al. 2020, Journal of Pediatric Urology)
Across 24,000 children, later training tracked with about 25 to 30 percent more bladder dysfunction.
Pooling 10 studies and over 24,000 children, training later was associated with more lower-urinary-tract dysfunction, including daytime wetting and bedwetting, with the risk rising after 24 months.
This is the highest-tier source on the downside of waiting. Li, Wen and colleagues pooled ten studies covering more than 24,000 children aged five to seventeen. Children trained at a younger age had significantly less lower-urinary-tract dysfunction, with a pooled odds ratio of 0.71. Training at or after 24 months was where the risk climbed.
The subgroups pointed the same way, less daytime incontinence and less bedwetting among earlier-trained children. The effects are modest, roughly a 25 to 30 percent relative difference, but consistent and robust to sensitivity analysis.
The caveat is that every study pooled here is observational, so this is a strong, repeated association rather than proof that delaying training causes the problems. Read it alongside the U-curve study below, which shows that forcing training too early is also a mistake.
24,121
Children pooled across 10 studies
OR 0.71
Less dysfunction with earlier training
24 mo
Where risk begins to climb
Why it matters
The best pooled evidence we have leans one way: children who come out of diapers later carry a somewhat higher chance of daytime accidents and bedwetting at school age.
This is one finding from the research library behind How to Birth a Mother. Everything here traces back to a study, a dataset, or a systematic review.