The moon, by its connexion with menstruation, and as the cause of the fertilizing dew, was regarded as exercising an influence over the entire animal and vegetable creation.
Remember, even though a home pregnancy test may claim to be accurate as soon as five days prior to your next menstruation date, the test will be significantly more accurate if you wait until a week after your missed period.
Freind (1675-1728) in his Emmenologia gave a mechanical explanation of the phenomena of menstruation.
One theory is that of "retrograde menstruation," where small amounts of endometrial tissue go backward through the fallopian tubes and travel out into the pelvis and abdomen.
Occasionally the hymen is imperforate and then gives rise to trouble in menstruation.