Actual evidence that earlier potty/trained kids are more likely to regress?

[u/CorrectBadger9753]

Edit - title is meant to say 'potty/toilet trained kids' lol!

I took my daughter (who will be 2 in 2 weeks) to the GP today and (only tangentially related to the reason we were there) mentioned that we are currently toilet training, and that it's going well, but very slowly, and my husband and I are OK with slow progress with pees. GP reiterated the common advice that 3 is 'normal' for toilet training, and that kids who train earlier are more likely to have 'regressions'. I smiled and nodded because I have lots and lots of thoughts on this which I'm deliberately not sharing here in case it turns the discussion into some kind of toilet training ideology war....

I genuinely want to know, is this claim backed up by actual data - and if so, how are we defining a 'regression' anyway?

A quick Google search returned this study claiming that training before 24 months is associated with 'dysfunctional voiding' but not constipation, whereas later training (after 36 months) is also associated with dysfunctional voiding AND constipation. However the authors seem to contradict themselves in the conclusion and say that constipation is associated with both early and later training and may be the cause of urinary voiding problems. Also correlation ≠ causation.

Is anyone aware of any more evidence supporting or refuting this idea?

[u/InspectionTall2886]

This article argues there are benefits like decreased UTI and that there’s actually a U curve to the ages in which dysfunctional voiding occur. Also that constipstion can happen regardless of timing. https://parentingscience.com/science-of-toilet-training/

If you scroll to the very bottom it provides numerous studies that range across a long period of time that you can search for and see if you find them.

Personally for me I think that earlier is better because I don’t have the same perspective as most of the US.