oPatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
The female reproductive system consists of the ovaries, Fallopian tubes, uterus, vagina and the vulva. At birth all the woman's immature follicles lie dormant in the ovaries. No more are produced. This is an important consideration - eg, in childhood leukaemias and chemotherapy, as they may need to be preserved to safeguard future fertility potential of the child.
- Puberty is a process of maturation of the sexual and secondary sexual characteristics, with menarche (onset of menstrual bleeding) as a step within that process.
- The ovarian follicles lie dormant from birth until puberty arrives and the rising hormones lead to the maturation of several ovarian follicles per month; usually only one matures and is released.
- Normal menstruation is the monthly cycle of blood loss per vagina, resulting from the breakdown of the uterine lining when implantation of a fertilised ovum does not occur. Menstruation is not a sign of ovulation, but of the fact that the hormonal controls and the reproductive tract's responses to it work.
- Normal menstrual loss is about 25 ml per day for 4-5 days per month. The amount of blood loss varies between individuals but tends to get heavier with age.
- Menarche is the start of the first menstrual period. Menarche has occurred at a younger age during the last century. This may be due to improved nutrition (and subsequent weight) in the population.
- The average age of menarche is 13 years, but it can be as early as 8 years and as late as 18 years and still be normal. Premature or delayed menarche should be investigated - ie before 8 years or after 16 years.
- Normal menstruation then occurs in a monthly cycle until menopause, unless interrupted by pregnancy.
The menstrual cycle is under the control of three sets of hormones:
- Gonadotrophin-releasing hormones - leutinising hormone-releasing hormone (LHRH) and follicle-stimulating hormone-releasing hormone (FSHRH)
- Gonadotrophins - luteinising hormone (LH) and follicle-stimulating hormone (FSH)
- Ovarian hormones - oestrogen and progesterone
The gonadotrophin hormone-releasing factors from the hypothalamus control the release of the pituitary hormones; the gonadotrophins - FSH and LH. They are produced by the anterior pituitary and control the ovarian hormones oestrogen and progesterone.
- During the follicular phase a rise in FSH from the pituitary stimulates the development of several follicles on the surface of the ovary. Each follicle contains an egg. Later, as the FSH level decreases, only one follicle continues to develop. This follicle also produces oestrogen.
- The LH peaks mid-cycle, triggering the release of the ovum - ovulation, which usually occurs 16 to 32 hours after the surge begins. The LH level falls a couple of days later.
- The oestrogen level from the ovaries increases gradually towards ovulation and peaks during the LH surge.
- The progesterone level starts to rise towards follicle release, preparing the endometrial lining of the uterus for implantation.
- Post-ovulation - the luteal phase - levels of LH and FSH decrease. The ruptured follicle closes (after releasing the egg) and forms a corpus luteum, which produces progesterone. If the ovum is fertilised, the progesterone levels are maintained by the corpus luteum and the endometrium is maintained.
- If the ovum is not fertilised the corpus luteum starts to degenerate and progesterone and oestrogen levels start to fall. The endometrial blood vessels constrict and the endometrial lining breaks down and is shed.
- The hormonal swings may be associated with changes in mood and libido, and with headaches in some women. However, some studies have not demonstrated good evidence for premenstrual mood symptoms.
- The first day of the cycle is counted as the first day of the bleed - Day 1. The cycle runs from the first day of menstruation to the next first day.
Natural family planning
- The mucus from the cervix becomes clear and runny (similar to egg white) about six days before ovulation, and drier and more viscous at ovulation. This change is called Spinnbarkeit and describes the ability of the mucus to be drawn/stretched. The basal body temperature also rises by a third to half a degree centigrade at ovulation.
- Keeping a note of these changes can form a simple, non-invasive method to time coitus for either pregnancy planning or pregnancy prevention - 'the rhythm method'. This term has been replaced by natural family planning.
- About 1 in 7 couples can have some problems conceiving a baby. However, over 8 in 10 couples having regular sex (every two to three days) will conceive within one year if the woman is aged under 40 years. In addition, of those couples who do not conceive in the first year, about half will do so in the second year. See separate article Infertility for more information.
Coping with normal menstruation
How a woman chooses to deal with the physical blood loss is a matter of personal preference. Modern developments of extra-absorbent disposable towels and discreet tampons have made managing menses easier.
- Period pains (dysmenorrhoea) respond well to anti-inflammatories - eg, mefenamic acid.
- Some women may need a combination of towels and tampons for overnight use, to prevent soiling bed linen.
- Sometimes women may wish to postpone their cycle because of holidays, etc. This can be achieved by:
- Norethisterone 5 mg tds.
- Tricycling the combined oral contraceptive pill (COCP); running packs together and omitting the pill-free week. This can happen for a maximum of three months.
Factors that may affect the menstrual cycle
NB: fertility can return before the first period after childbirth.
- Breast-feeding can delay the return of normal menstruation postpartum, particularly if exclusive and may form the basis for the lactation amenorrhoea method (LAM) of contraception for the first six months of the baby's life.
- Rapid weight change - increase or decrease.
- Body weight below a certain level - eg, in eating disorders - particularly anorexia nervosa.
- Emotional stress - eg, fear of pregnancy/phantom pregnancy.
- Significant Illness.
- Drugs - eg, hormones, cytotoxics.
- COCP - this causes an artificial withdrawal bleed - ie early menopause or pregnancy can be masked.
- Normal menstruation can be affected by any failure of the clotting system in the body.
Toxic shock syndrome
This is a toxin-mediated disease characterised by fever, rash, hypotension, constitutional symptoms and multi-organ involvement. See separate article Toxic Shock Syndrome for more information.
Further reading & references
- Sultan C, Gaspari L, Kalfa N, et al; Clinical expression of precocious puberty in girls. Endocr Dev. 2012;22:84-100. doi: 10.1159/000334304. Epub 2012 Jul 25.
- Romans SE, Kreindler D, Asllani E, et al; Mood and the menstrual cycle. Psychother Psychosom. 2013;82(1):53-60. doi: 10.1159/000339370. Epub 2012 Nov 6.
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
|Original Author: Dr Hayley Willacy||Current Version: Dr Louise Newson||Peer Reviewer: Dr John Cox|
|Last Checked: 07/06/2013||Document ID: 2520 Version: 22||© EMIS|