Babies Can Learn Early: Bladder Control in Vietnam vs Sweden (Duong et al. 2013, Journal of Pediatric Urology)
Early-trained babies reached full bladder emptying around 9 months, versus 36 months for late-trained Swedish peers.
In a culture that starts in early infancy, 89 percent of babies are on daily potty training by six months and empty their bladders fully by around nine months. Swedish babies, trained late, first reached full emptying at around 36 months.
Duong and colleagues compared 47 Vietnamese children, raised in a tradition that begins potty training in the first months, with 57 Swedish children trained the conventional late way. By six months, 89 percent of the Vietnamese babies were on daily potty training. By two years, 98 percent were finished. In the Swedish group, only 5 percent had even started by 24 months.
The striking physiological finding is that the early-trained babies showed complete bladder emptying, no residual urine, by around nine months, while the Swedish children first reached that point at around 36 months, with fewer voids and lower volumes (p < 0.001). Early, responsive elimination did not appear to harm bladder development. If anything it tracked with earlier, healthy bladder maturation.
The catch is that this compares two whole cultures, not a randomized trial, so other differences between them could play a part. It is the cleanest published signal that starting early is genuinely feasible and physiologically fine, not proof that it causes the difference.
89%
On daily potty training by 6 months (Vietnam)
5%
Started by 24 months (Sweden)
9 vs 36 mo
Age at full bladder emptying
47 vs 57
Children compared
Why it matters
Starting in the first months is not exotic or harmful. In a whole population that does it, most babies are participating by six months and their bladders develop just fine.
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.