If expense was the main thing limiting fertility, you’d expect that fertility would be positively related to income, but the reverse is true.
There have been some interesting changes over the last 20-40 years in that regard.
https://www.imf.org/en/Publications/fandd/issues/Series/Anal...
If expense was the main thing limiting fertility, you’d expect that fertility would be positively related to income, but the reverse is true.