That’s the case for white, non-Hispanic ones.
In 1970 there were about 3 million white births, of which 400k or so were Hispanic probably (the number has to be inferred because “all other” was around 500k and included Asians). There were something like 600k or 700k college mom births then to non-Hispanic white mothers. About 500k from reporting states and again, the rest is an estimate from non-reporting states.
There are still about 3 million white births these days (2015), but about a million of them are Hispanic ethnic groups who identify as white racially. Of the remaining two million non-Hispanic white births, about 1.5 million come from college moms.
So non-Hispanic white moms went from producing about 2.5 million births in 1970 to producing about 2 million births 45 years later. But college moms went from a modest but decisive minority of births to a supermajority in about 2 generations. And non-college moms have steadily been foregoing childbirth at all.
What’s fascinating about this is that college is mildly natal for white non-Hispanic women, since they’re the ones having more and more rather than fewer and fewer raw births. College mom fertility is fairly stable, with 15-25% childless rates being offset by the remaining women having 2-4 kids to generate a pretty reliable almost-2 kids for the group “college women”.
For BAs and up, the births quadrupled in that timeframe, outpacing the general trend of simply attending and completing college at higher rates. While there is higher attendance among women these days, the proportion of births born to college moms (completing or not) is higher than that baseline.