A woman’s menstrual cycle matches the moon’s 29 day cycle, and although many woman start and stop at different times. Without artificial light, many women’s cycles will follow closely to the cycles of the moon’s phases.
Other factors might screw things up such as stress, medication, exercise and even diet. The loss of blood each month is why women need extra iron, for instance.
Many cultures believe this time of the month makes a woman ‘unclean’. Such as Orthodox Jewish tradition of Niddah, where the woman must ritually bath after her cycle is complete..
Some groups believe a menstruating woman should not participate in magick or ritual. When I first read this, the author reasoned that women are powerful at this time, that any blood in ritual detracts from the forces already present.
I disagree. I feel there’s a time and place, and with a woman undergoing a time of cleansing, she has more power in regards to banishing and removing the bad things in her life at that time. Its important to listen to your body. If you’re dealing with PMS or cramps, you might not want to perform ritual.
If you otherwise feel fine, I say go ahead. Take note of outcomes of magic and meditation performed during these times as well, to see if there is a pattern.
I personally feel that the rules setup by culture or religion doesn’t work for the individual. Take for instance “Mercury in Retrograde”, for people who have Mercury in their sign, it may not affect them as it affects others.
As always, go with your heart (and soul).