The short answer is that it was rather later in previous centuries than it is now. The reason is that women both started and finished menstruating later: something to do with the quality of nutrition, I believe.
So whereas birth in one's 40s would now be considered late, it was common in previous centuries, and the oldest case I have come across is a woman giving birth at 52, although that is definitely unusual.
Stories of Pregnancy over 44 years old - sharing stories I find online, for inspiration!
You Can Get Pregnant in Your 40's - Sharing articles, discussing options & suggestions
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