I had never heard of this before reading Gone with the Wind.
It's not accurate - this myth arises out of a misunderstanding of the term "confinement" (used as a euphemism for childbirth at the time) and early twentieth century anti-Victorianism. There is always more to be said, but you may be interested in some previous answers of mine:
How did polite Victorian ladies refer (even among themselves) to a late or missed period?