On this page a brief outline of the Menstrual Cycle is given and further information is available by clicking on the topics listed at the bottom of the page.
Brief outline of the Menstrual Cycle
The menstrual cycle is the fertility cycle of the woman during the child-bearing years. The first day of the menstrual cycle is the first day of the period and the last day of the menstrual cycle is the day before the next period. The cycle length varies from 23 to 35 days, the average length is about 28 days.
During each cycle an ovum (egg) matures in the ovary and is then released into the fallopian tube ready to be fertilised. The release of a mature egg is called ovulation. (Link to Fig. 6.10 ovulation). While the ovum (egg) is maturing the lining of the uterus becomes thicker and more vascular in preparation for a possible pregnancy. If fertilization of the ovum does not occur in that cycle menstruation will start about 14 days after ovulation.
What is menstruation? Menstruation is the vaginal bleeding that occurs at the end of an ovulatory cycle when fertilization has not occurred and is due to the drop in hormone levels in the bloodstream. During the menstrual cycle the lining of the uterus proliferates to prepare for a possible pregnancy due to the actions of the hormones, oestrogen before ovulation, and progesterone after ovulation. Progesterone maintains the lining of the womb and when pregnancy does not occur the progesterone level falls causing the lining of the womb to be shed about 14 days after ovulation. This shedding is called menstruation, it marks the beginning of a new cycle, and lasts 3 to 5 days. (when menstruation starts the woman knows in retrospect that ovulation most likely had occurred 14 days previously.)
Ovulation: Ovulation means the release of a mature ovum from the ovary into the fallopian tube. It occurs once in any cycle, about 14 days before the next period. If two or more ova (eggs) are released in a cycle, all are released within the same 24 hour interval. The ovum lives for 24 hours. Despite the short life-span of the ovum the fertile phase of the cycle is further increased by the ability of sperm to survive in fertile-type cervical mucus for 5 days; fertile-type mucus is present in the days before ovulation.
Menarche: The first menstrual period is known as menarche and usually occurs about 13 years of age. The normal age of menarche varies from 10 to 16 years. A study done in Ireland of 2940 girls aged 9 to 17 years showed that the average age of menarche in Ireland is 13.5 years, with a standard deviation of 1.3 years.1 The age of menarche has decreased in the 20th century and this could well be due to improved nutrition. In the 19th century girls in the USA reached a weight of 46kg at about 14 years of age which was the year of the menarche. In Belgium in the 19th century girls reached a weight of 46 kg at about 16.5 years and also attained the menarche at that age. According to Griffin et al,2 the increase in body fat at adolescence of about 11kg is equivalent to 99,000 calories and the number of calories estimated to maintain a pregnancy is 88,000. Thus one of the main functions of the adolescent growth spurt in females may be the storage of energy to sustain a pregnancy and lactation.
After the final menstrual period has occurred the woman has reached menopause, and the end of the child-bearing years has arrived. Menopause occurs within a wide age range between the ages of 42 to 58,3 on average at about age 51 and this is unchanged from ancient times. (Link to Menopause)
What factors can cause irregularity of the menstrual cycle? The menstrual cycle is regulated by a finely tuned balance of hormones secreted by the ovary and the pituitary gland, and is ultimately under the control of the higher centres of the brain. This delicate mechanism can be disturbed by a number of factors, notably stress, but also by over-doing physical exercise, by dieting and by weight-loss. Women taking hormonal contraception (the Pill) do not have a normal menstrual cycle and the apparent menstrual period when taking the Pill is just a withdrawal bleed due to a drop in synthetic hormone levels in the blood in the pill-free days.
1 Hoey, H.; The age of Menarche in Irish girls; Ir Med J. Oct. 1986, vol 79, no. 10, p283-285
2 Griffin, James E; Ojeda, Sergio R; Textbook of Endocrine Physiology, 3rd edition, 1996, ch. 9, p187, 188
3 Soules MR, Sherman S, Parrot E et al; Executive summary: Stages of Reproductive Aging Workshop (STRAW). Fertil Steril. 2001; 76: 874
- What is the Menstrual cycle (6a)
- The ovary and uterus during the cycle (6c)
- Factors necessary to achieve pregnancy (6e)
To be most effective, the woman must be taught the Symptothermal Double-Check Method of Natural Family Planning by a qualified natural family planning teacher.