There is something fundamentally wrong with the trainer and I'm having trouble figuring out which option does it, but using the trainer prevents births.
So far I have confirmed it's not the "stop aging" option (which seemed like a logical option to test). Even on a new save where this function was never used, births don't happen. When I press F2 and hover over adult females, it tells me I have 9 females, out of which 17 are pregnant. Basically, they seem to carry forever, until they get old and die, along with the unborn child.
This is extra frustrating, considering I'm going for an achievement, where I need a population of 100 in the first era. Just the immigration isn't enough to counter the birthrate of 0, which caps me at around 50-60 population... forever.
I am having the same issue. People and animals do not give birth.
Have you found out what exactly triggered it?