Should women rest from practicing youga during their menstruation? Many say so, but others disagree. Some say that certain asanas should be avoided, while others are beneficial particularly during this time.
One who argues that women should rest during their menstrual period is Pattabhi Jois, the founder of the ashtanga yoga system, who prescribes three days of complete rest. He means that the body goes through a lot of dramatic changes while a woman is bleading and that the vigorous practice of ashtanga may interfer with this purifying process. He also says that the uppwards contraction of the bandhas as practiced during yoga is contrary to the natural downward movement of menstruation.
Other female longterm ashtanga practitioners maintain practice during their period and says that it helps them with problems as menstural cramps etc. Some women like to take a break from practice during the first day of their cycle but continues with a modified practice, avoiding inversions while bleading. Avoiding inversions is also tied to the idea of not wanting to change the natural flow of the menstruation and is recomended by for example Geeta S Iyengar. She also recomends avoiding armbalanding postures, bound postures and postures with abdominal contraction while she recommend specific postures to relieve problems related to menstruation, see her book Yoga a Gem for Women.