Prosperity doesn’t make fertility drop, it makes it less necessary to have children because:

• Parents don’t need to have 5 children just for 1 or 2 to survive… people can have 1 or 2 children and expect them to survive now.
• Adults don’t need children to survive. Before people expected their children to help them survive when they are elderly so the kids can work the farm and the grandparents can babysit grandkids in their multigenerational home. Now nursing homes can take care of your needs after saving enough money.
• Now that women are gaining equal rights, they can choose to be other things than just a mother or a wife. Life can be full and satisfying without kids now.

But I do agree people can feel that working and being a mother is too much, and decide not to have kids as well.

If you make a society where everyone HAS to work in order to survive but also provide no public childcare, schooling and healthcare then obviously people are not going to be able to afford to have babies.

Ain’t urbanisation made fertility drop tho? Like raising a child in the city is bloody expensive while in the country extra child is spare hands for work

I don’t really know, but as far as actual fertility(the ability to become pregnant, rather than just birth rates (the rate at which people have children). It is more likely to be down to pollution like microplastics and lead in the water and the like.

Possibly even rising temperatures, don’t spermatozoa die above 78°F/25.5°C? So if men can’t cool off their junk, they can’t get anything worthwhile delivered to the egg? I’m no biologist so I’m iffy on that one.