Years ago, radio 4 had a fascinating programme about this practice and the infertility issues it could cause if a woman ovulated early in her cycle.
Today reading about this practice in Nepal where you can die of exposure made me realise it may be a more common practice than I realised.
www.nytimes.com/2019/01/09/world/asia/nepal-menstruation-taboo.html
Are women considered unclean when the result of this nine months later is a beautiful child??