The menstrual cycle is by far one of the most elegant physiologic phenomena occurring in the woman.
Normal menstruation is defined as the periodic efflux of the sloughed endometrium and blood out of the uterine cavity into the vagina and ultimately outside of a woman’s body. There are many different cultural beliefs, myths, and taboos, even within educated countries, about the purpose and function of the menstrual cycle. For adolescent girls, it is an obvious sign of pubertal development and signifies the passage into womanhood and the capability and responsibility of reproducing. Monthly menses become for many women a reassuring sign that they are not pregnant, if conception was not desired, or a cause of frustration and disappointment if pregnancy was desired. Functionally the ultimate aim of the human menstrual cycle is the development of a mature oocyte that is ovulated and fertilized. Ultimately, if fertilization is successful, implantation of a dividing embryo into the receptive endometrium of the uterus occurs.
Menarche, the age at onset of menstruation averages 12.8 years. The normal age range for menarche is 10 to 16 years.
The idealized length of the normal human menstrual cycle is 28 days from the onset of bleeding until the next episode of bleeding. There is great variability in menstrual cycle length; an interval of 24 to 35 days is considered normal.
The amount of bleeding also varies widely in the number of days of bleeding and the amount of blood lost. The number of days of bleeding ranges from 2 to 8 days, but the usual length is 4 to 6 days. The average amount of blood lost with each menstrual cycle is 30 mL, and the normal range is 25 to 60 mL Even this relatively small amount of blood loss can lead to iron deficiency anemia if adequate iron is not ingested or absorbed. Blood loss of greater than 80 mL is excessive and commonly leads to iron deficiency.
Ovulatory woman individually have consistent menstrual cycle lengths and number of days of bleeding. There is some cycle length variability for most women, however even in a woman with regular menstrual cycles variation by 2 days in length can be seen in one third of their cycles. This variation in cycle length is attributed to the variability in the length of the follicular phase of the cycle. The luteal phase consistently is 13 to 15 days in length after menarche and remains consistent until the perimenopausal period. Great variability is seen at the extremes of reproductive life, with adolescents and perimenopausal women experiencing wide fluctuations in menstrual cycle length and the number of days of bleeding because of their tendency to experience anovulatory cycles. Adolescent girls average menstrual cycle lengths of 34 days. There is a gradual decrease in cycle length until women reach their late 30s or early 40s, when cycle length averages 27 days. Anovulatory cycles frequently begin when a woman reaches her late 40s. Cycles lengthen again and average 33 days beginning 3 years before menopause.
Significant variation in the menstrual cycle length or number of days of menses commonly leads to reproductive-age woman to seek medical advice. Pregnancy-related reasons for alterations in menstrual cycle length are the most common reasons for alterations in menstrual cycles in reproductive-age women. Lactation and abnormal pregnancies always must be ruled out as reasons for a change in menstrual pattern in every woman who seeks evaluation.
The normal menstrual cycle is best conceptualized by focusing on the physiologic effect of the two main organ systems involved in menstrual function –the uterus and the ovary. The menstrual cycle classically is divided into phases. These phases are a convenient way to examine what is happening at different times at the level of the two main organ systems.
The first phase of the menstrual cycle is called the follicular phase at the level of the ovary and the proliferative phase at the level of the uterus. The follicular phase ends with the onset of the luteinizing hormone (LH) surge. Ovulation occurs in response to the LH surge. The next phase of the menstrual cycle , which begins after the onset of the LH surge, is called the luteal phase at the level of the ovary and the secretory phase at the level of the uterus.
With this excellent explanation provided by Dr, Randal Robinson in the book “Reproductive endocrinology and infertility” we have a great explanation of what the menstrual cycle is and what it is involved on it.
Have a look at the ovulation calculator to have a go and get a good explanation of how to use it. It is really easy.