Every month there are many articles about "the cycle of the moon and the cycle of the menstruations" in the newsgroups...
It seems normal that women have very irregular periods (without using the pill)
It seems that the week is defined as the maximum-time of an average period
It seems that this happens about every month
Menstruation seems to be related to 'mensa', i.e. moon(th)
It seems that there are about 12 full moons every year
It seems that the moon, the menstruations and the months were in harmony before the industrialisation
So it becomes clear that a moon-cycle or a menstruation-cycle of 28 days is WRONG,
since 13x28days=364days and since DECEM(ber)=10
So I think that the pharmacy used dirthy tricks to convince the women that they were abnormal and to propagate the pill...