It strikes me that winstoninabox's analysis of Japanese birthrates is almost blindingly self-evident.
Maybe economics is all important, and culture only has a feeble indirect influence. What does the worldwide correlation between birthrates and female workforce participation look like, O Economist-reading Marco? And are the outliers chiefly countries that have gross income inequality and/or completely socialised everything, enabling affordable child care?
This is not to argue that we should keep women out of the workforce, anymore than the [abortion = less crime] equation is an argument that we should permit abortion, or the [carbon dioxide emissions = global warming] equation is an argument that we should reduce carbon dioxide emissions; it is just something we need to keep in mind and manage.
Ultimately I am sure there will be a simple technological fix, as with most problems. Either a drastic extension of the useful human lifetime or the popularisation of a degenderised human phenotype should be sufficient.