For example, if miscarriages are criminalized, and access to birth control is restricted - both real things that have been attempted or have actually happened in the US as a part of anti-choice policies - the only safe choice is to not have sex, ever. Which means you're probably never going to have kids, instead of before where there was a chance you'd get pregnant and then decide whether to have the child or not. Now it's too risky to even have a chance of getting pregnant if you have no autonomy. I certainly would never risk it in a state with anti-choice policies.
The intent of these policies might be to raise the birth rate, but I'm not sure they're going to do that. We'll see, I guess.
IMO the demographic crisis is more likely to be influenced by other factors, like the rising costs of raising children, the increasing constraints and pressures on parents, etc. But those policies don't help.
The decision to have kids should be a deliberate commitment between the parents, not some kind of lottery where one falls pregnant then decides what to do next.
It's better not to fall pregnant at all otherwise