Over the last three decades, US birth rates among women under 25 declined while birth rates among women over 30 increased, dramatically so among women over 40. It's well known that mean maternal age at birth has increased substantially in the West over the last 60 years.
What might not be as widely recognized--I previously wouldn't have guessed as much--is that in 1950 absolute birth rates among American women over the age of 40 were substantially higher than they are among women over the age of 40 today (on the order of 50% greater). This even though a larger percentage of total births today are to old matrons than was the case in the middle of the 20th century.
Even with all the fertility treatment cheats, longer life expectancies, and bodies less battered by previous childbirths that middle-aged women enjoy today over what their grandmothers dealt with, the latter remained more fecund than the former all the way up to menopause.