Menstruation, which is the evidence of sexual maturity, is a monthly hemorrhage from the uterus which escapes through the vagina, normally recurring throughout the entire child-bearing period, except during pregnancy and lactation. The duration of this child-bearing period, or sexual activity, is about thirty years and continues from puberty to the menopause.
The frequency of the menstrual periods varies in different women from twenty-one to thirty days, but the normal interval between periods is twenty-eight days, which corresponds in point of time to the menstrual cycle. Thus it is usually four weeks, or a lunar month, from the beginning of one period to the beginning of the period following, making thirteen menstrual periods during each calendar year.
Just why menstruation occurs about every twenty-eight days is not known, but the belief is that, although menstruation is in some way dependent upon ovulation, its periodicity is regulated by the corpus luteum. It is also believed that the corpus luteum of pregnancy holds menstruation in check during the nine months of gestation.
The menstrual cycle is divided into four stages, and though there is not entire unanimity of opinion concerning the changes which take place during these four stages, the preponderance of evidence is in favor of the following processes.
The first or constructive stage lasts about seven days. It is during this stage that the preparative changes, which have been described, are made for the reception of the matured ovum. The uterus becomes engorged with blood and is somewhat enlarged and softened as a result. The endometrium grows deep red, thick and velvety, partly because of the greatly augmented blood supply, and partly because of an actual increase of connective tissue in its structure. There is also an increase in the size and activity of the uterine glands and in the amount of their secretions. If the ovum remains unfertilized, which is usually the case, it does not attach itself to this elaborately prepared lining, but passes out with the uterine discharges, and all of this preparation and increased vascularity not only go for naught, but must be undone.
The second stage, therefore, which lasts about five days, is the destructive stage, during which the newly developed tissues are broken down and the menstrual discharge occurs. During this period the greatly increased secretions of the uterine glands mix with the blood that oozes from the engorged endometrium and with the disintegrated uterine tissues, and pour from the vagina as the menstrual flow.
The third, or reparative stage, which follows, occupies about three days. During this stage the destroyed uterine tissues are regenerated by new growth from the deeper, uninjured tissues, and the entire organ returns to its normal state.
The fourth, or quiescent stage, now follows, the damage having been repaired, and lasts twelve or fourteen days. This is the time remaining before Nature with unwearying patience begins all over again to prepare for the reception and attachment of the next matured ovum, in case of its possible fertilization.
It will be seen that the duration of the menstrual period, which is coincident with the destructive stage of the menstrual cycle, is about five days, but it is entirely within normal bounds if it varies in length from two to seven days.
The discharge is usually scant at the beginning of the period, increasing in amount until about the third day, after which it diminishes steadily until its cessation. The normal odor of this discharge, consisting as it does of blood and uterine secretions, has been likened to that of marigolds.