Is Hypofertile trait a 0% chance?

[rrrW]

Hi folks! I was hoping the Hypofertile trait was sort of a "super low but not 0" chance thing, and assumed as much, given it's not called "Infertile", but based on evidence I suspect it really is a 0% thing
Can anyone confirm which is true?

And, is there any way to modify that in my game so it would be say, 0.01% chance or some player defined buckets of range from "0% / Tiny % / Same as if you used birth control, when you aren't using any birth control" or the like?

[extrashot]

There are settings to change the fertility level. I have it set on the highest level, extreme. Right now I'm playing a household with a couple that I gave the hypofertile trait to. The stats say the guy has a 2% "can impregnate" chance, and the girl has a 1.71% chance "can get pregnant." So I'm sure if I had the fertility level set to normal that it would be pretty much zero.