[myrmidon]

This sounds extremely plausible to me, but I would be very careful about conclusions from such studies, because I believe the general expectations of society as a whole regarding child-raising matter a lot and you can't easily quantify that.

Anecdotally, when my grandmother did not birth a child for two consecutive years in her thirties the village priest came to investigate (!!). Expectations have shifted massively since, and the single/dink lifestyle is way more "acceptable" now.