Scientific information that connected menstruation with ovulation was a mid-18th century discovery. Before this time, most explanations of periods were based on observations. These observations such as blood flow from the vagina and pain because of abdominal cramps during periods were explained differently in different ancient societies. In some cases, blood represented life and fertility while in others, blood and pain represented danger that must be paid proper attention to.

The continuation of these different ways of ancient thinking in the absence of scientific information in our current societies causes menstrual myths. Talking about periods is still treated as a taboo in many societies. There is a lack of awareness and information about it. So, these myths continue to live on and are not questioned from one generation to another.

Illustration of a girl whispering to another girl presumably a menstrual myth - Menstrupedia
References:
  1. The discovery of the ovaries, http://ovary.stanford.edu
  2. Psychology of Infertility, http://www.cambridge.org
  3. Janice DeLaney, Mary Jane Lupton, Emily Toth (1988), The Curse: A Cultural History of Menstruation
  4. Naomi Janowitz (2002), Magic in the Roman World: Pagans, Jews, and Christians