> It seems to be inversely correlated with first world living status and education more than anything.
Well, at least for Germany I can provide some anecdata: either you're on welfare and have the state fund your life including kids or you're rich. The middle class and especially the young (20-30y) population in the major cities simply often cannot afford kids, not with the exploded rents and the trend to unpaid (!) internships, year-limited contracts, "gig work" and other things making my generation's life a living hell. I'm 27 and lucky to have landed an unlimited employment contract. The whole situation reminds me more and more of the setting of Idiocracy, and that without the US president in that movie being obviously inspirational for the current real world one.
In addition the young population that fled the rural areas (due to e.g. job availability, the lack of public transport, any form of Internet faster than ISDN, ...) but left their parents/grandparents behind cannot rely on them to help with bringing up a child, further lowering the birth rate.
For Italy, the situation is even worse - depending on the source and demographic target, up to 70-80% of young people still live with their parents because they cannot afford their own home (https://www.thelocal.it/20161024/two-thirds-of-italian-mille...). Hard enough to... uh, get going with your partner when your parents are next room, much less actually wanting to raise a child.