Menstrual cycle is a specific time period which starts from the 1st day of menses and terminates on the last day before the next menstruation begins. As a rule, a menstrual cycle lasts from 21-35 days. An ideal cycle is 28 days. A woman may have different duration cycles (no more than 4 days to the one or the other side). Such cyclic bleedings in girls usually start between the ages of 11-13 and last till 47-50 years on average, up to menopause and gradual reproductive function loss. These facts are known, but there are some other points one should know in case of planning a pregnancy or just to examine your body thoroughly.
- Fertile days
- Cycle – 28 days
Follicular phase starts at the moment a new menstrual cycle begins. The principle hormone of this phase is follicle-stimulating hormone, FSH to launch and maintain a process of follicles maturing. In general, 5-7 follicles start maturing; as a result the one, to have reached 14 mm, becomes dominant and continues maturing; the rest endure regression. Duration of the follicular phase (the growth of a dominant follicle) may vary from 7 up to 20-22 days.
Within this period FSH level and sizes of the maturing follicles with an egg cell inside it are increasing gradually. Apart from the growth of follicle, one more important process happens – dead endometrium removal from the uterine cavity. It comes out with blood. This process is called menstruation and will be started after estrogen and progesterone levels lower in the blood up to critical marks at the end of a previous cycle.
After purification of a womb from the old mucous membrane and termination of menstrual discharges, a process of new endometrium development and thickening begins. This endometrium is stimulated by estrogens which are produced in the ovaries. By the time ovulation comes, mucous membrane of the womb is getting ready to accept a fertilized ovum. Thus, it is possible to distinguish three main events of this phase:
- Purification of uterine walls.
- The growth and follicle maturing.
- Gradual rising of new endometrium.
It is believed that the duration of ovulatory phase is a period when an egg cell is ready to be impregnated, i. e. about 48 hours. According to different sources such period lasts from 2-5 days. Within the previous phase, follicle and an egg cell inside it reach its upper limit sizes. At this period the follicle breaks, and mature egg cell exits towards the uterine tube. The process is called ovulation. Luteinizing hormone favors this process. It stimulates a production of special agents, required for weakening and explosion of a mature follicle wall – graafian follicle, ready to be broken, letting an egg cell. LH level and concentration are sharply increased in blood at the moment this phase comes; FSH level is being reduced.
An egg cell passes along the uterine tube due to twinkling movements of lanate epithelium to line tubes inside; then it is going to be impregnated or implanted in endometrium. The other variant is dissolution of an egg cell in endometrium after some time. Anovulatory cycles don’t include such a phase. They are considered to be single-phase and monophase. At the same time, follicles are maturing step-by-step and dissolving instead of breaking.
After termination of the ovulatory phase, a lutein, or yellow body phase comes. It lasts for 14 days (10-16) in spite of physiological menstrual cycle type of a healthy woman. When this phase ends, menstruation or pregnancy begins. It depends on the fact, whether an egg cell was impregnated or not. After bursting of the follicle, it turns into a yellow body – a unique temporal gland to produce progesterone which makes a womb ready for a potential pregnancy; the yellow body is also responsible for maintenance of pregnancy. The lutein phase increases basal temperature over 37ºC. It happens due to progesterone. That means, in case of ovulation absence, a temperature won’t be increased. The lutein phase is also known as secretory one, as far as edometrium glands are ready to produce a specific nutrient secretion under the impact of a progesterone at this period. Such secretion is vitally important for the embryo growth and its development. High level of progesterone and estrogen in blood is a reason of enlarged channels in mammary glands. As a result, FSH and LH production goes up notably.
In case ovum fertilization hasn’t happened, the yellow body starts dissolving. It also leads to progesterone and estrogen level reduction up to a definite mark (in 10-12 days after ovulation). Thus, endomentrium rejection happens and menstruation begins. It is also triggered off by augmented number of prostaglandins to affect uterus and vasospasm decrease. In case of ovum fertilization, the yellow body, attended by chorial gonadotropin, continues functioning and producing of important hormones up to placenta formation.
So, this is a description of the normal course of a menstrual cycle. If some phase undergoes a malfunction, there is a threat of pregnancy loss. In case you have noticed some dysfunctions in your menstrual cycle, it advisable to have a medical examination.