Elaine Goodfriend, who edited the commentary to accompany the portion Metzora in The Torah: A Women’s Commentary,* notes a number of reasons that menstruation was probably less common for ancient women compared with contemporaries:
sparser diet and later onset of menstruation;
earlier marriage and more pregnancies;
breast-feeding for 3 years (based on biblical stories).
I have read similar comments over the years. Was menstruation regarded in the ancient world, then, as out-of-the-ordinary, rather than a regular, natural process for women? I don’t know the answer, but it could explain much of the disconnect between the biblical and the modern understanding of women’s bleeding/discharge.
* Please see Source Materials for full citations and additional information.
The “Opening the Book” series was originally presented in cooperation with the independent, cross-community Jewish Study Center and with Kol Isha, an open group that for many years pursued spirituality from a woman’s perspective at Temple Micah (Reform). “A Song Every Day” is an independent blog, however, and all views, mistakes, etc. are the author’s.