The menstrual cycle is the time between the first day of one period and the first day of the next one. The usual length of the cycle is 28 days, though this can vary.
What is happening to your hormones?
At the start of the cycle, your pituitary gland (a small gland in the brain)produces a hormone called FSH (follicle stimulating hormone). This stimulates the formation of a follicle (a small cyst containing an egg) in the ovary.
At this stage, the ovary is producing a single hormone, oestrogen. In the middle of the cycle, the pituitary produces a large amount of a different hormone called LH (luteinising hormone), which causes the follicle to rupture and release the egg (ovulation).
From this point onwards, the ovary produces two hormones: oestrogen and progesterone. If no pregnancy results, the levels of progesterone start to fall; this drop in progesterone triggers a period.
How do you know when you're ovulating?
Some women get pain on ovulation, but for the majority, there is no indication that ovulation has occurred. The alteration in hormone balance around ovulation causes a small change in basal body temperature, and a change in the consistency of cervical mucus, and these changes can be monitored by those who are trying to conceive.
What about PMS?
Premenstrual syndrome is a group of symptoms affecting up to 90% of women at some point during their menstruating lives. As tension, mood swings and irritability are prominent symptoms, the condition used to be called PMT (premenstrual tension). Since other symptoms have been recognised as having the same hormonal basis, the wider term PMS is now being used.
Other common symptoms include breast tenderness and swelling, headaches, bloating, palpitations, sleep problems, tiredness, sugar cravings, achy legs and fluid retention.
PMS symptoms typically start between three and ten days before each period, and dramatically improve as soon as the period starts, or within a day or two. Diet and lifestyle measures can help many women to control the symptoms.
Painful periods
Period pain is a common problem, especially in young women. It is caused by spasm in the uterus during menstruation, and is known medically as spasmodic dysmenorrhoea. It tends to be worse when the periods are heavy and clotty, and can be accompanied by faintness and nausea and vomiting. It tends to improve after childbirth.
Prescription medicines are available for those whose pain isn't relieved by simple, over-the-counter painkillers and a hot-water bottle. The contraceptive pill can also be used very effectively to alter the nature of the period.
Period pain that develops for the first time after years of painless periods should be reported to the doctor, and may require further investigation. This is known as secondary dysmenorrhoea, and often starts a few days before the period begins. The pain tends to be dull and constant, rather than coming in spasms. This pattern of period pain may be due to a medical problem, such as endometriosis or pelvic inflammatory disease.
