Female hormones

From puberty onwards, LH, FSH, oestrogen and progesterone all play a vital part in regulating a woman's menstrual cycle, which results in her periods. Each individual hormone follows its own pattern, rising and falling at different points in the cycle but together they produce a predictable chain of events. One egg (out of several hundred thousands in each ovary) becomes 'ripe' (mature) and is released from the ovary to begin its journey down the Fallopian tube and into the womb. If that egg isn't fertilised, the levels of oestrogen and progesterone produced by the ovary begin to fall. Without the supporting action of these hormones, the lining of the womb, which is full of blood, is shed, resulting in a period.

Pregnancy
If the egg released from the ovary is fertilised and a pregnancy results, a woman's hormones change dramatically. The usual fall in oestrogen and progesterone at the end of the menstrual cycle doesn't occur, so no period is seen. A new hormone, HCG (human chorionic gonadotrophin), produced by the developing placenta, stimulates the ovaries to produce the higher levels of oestrogen and progesterone that are needed to sustain a pregnancy. Most pregnancy testing kits are designed to detect HCG in a woman's urine, and many can pick up even small amounts just a day or so after her first missed period.

By the fourth month of pregnancy, the placenta takes over from the ovaries as the main producer of oestrogen and progesterone. These hormones cause the lining of the womb to thicken, increase the volume of blood circulating (in particular the supply to the womb and breasts), and relax the muscles of the womb sufficiently to make room for the growing baby. Around the time of childbirth, other hormones come into play that help the womb to contract during and after labour, as well as stimulate the production and release of breast milk.

After childbirth
After childbirth, what then? Levels of oestrogen, progesterone and other hormones fall sharply, causing a number of physical changes. The womb shrinks back to its non-pregnant size, pelvic floor muscle tone improves and the volume of blood circulating round the body returns to normal. The dramatic changes in hormone levels might also play a part in causing postnatal depression, although no real differences have been found in the hormone changes of women who do, and do not, get postnatal depression. It may be that some women are more easily affected by these hormonal fluctuations than others.

Talking of hormonal fluctuations, although they have been the subject of study for many years, we still don't know whether they are responsible for the wide range of physical and psychological symptoms we now call premenstrual syndrome or PMS. No-one doubts that many women experience tender breasts, abdominal bloating, irritability, low mood and other symptoms in the lead up to a period but whether these are due to hormone fluctuations, changes in brain chemicals, social and emotional problems or a combination of all three is a matter of debate.

The menopause
The next significant hormonal change for most women occurs around the time of the last period - the menopause. Over three to five years leading up to a woman's last period, the normal functioning of her ovaries begins to deteriorate. This can cause her menstrual cycle to become shorter or longer, and sometimes it becomes quite erratic. Periods may become heavier or lighter. Eventually, the ovaries produce so little oestrogen that the lining of the womb fails to thicken up and so periods stop altogether.

For most of a woman's life, oestrogen helps to protect the heart and bones, as well as maintaining the breasts, womb, vagina and bladder in their healthy state. The marked loss of oestrogen in a woman's body that occurs around, and after, the menopause can, therefore, have detrimental effects on her health; as well as causing uncomfortable symptoms such as hot flushes and night sweats, lack of oestrogen can increase the risk of heart disease and the bone disorder osteoporosis. Other problems include vaginal dryness, discomfort during sex, recurrent urine infections and incontinence. It may also contribute to the depression, irritability and poor concentration, which some menopausal women experience. But the menopause doesn't have to be a disastrous time for women - if reduced hormone levels do cause unpleasant symptoms, treatments such as hormone replacement therapy (HRT) are often very effective. HRT and other types of medication can also be used to prevent health problems, for example if a woman has a significantly increased risk of developing osteoporosis or heart disease in the future.

So, from the cradle to the grave, hormones play an important role in every woman's life. They shape our bodies (quite literally) as well as some of the most important events we experience, from pregnancy and childbirth to the menopause. There may be times when you curse your body's hormones, but console yourself with the thought that life without them would be much less interesting!