The ABC of menstruation

The normal cycle
Working out your ovulation
The fertile window
Changes and variations

Menstrual periods are a natural response to the hormone changes of the menstrual cycle and ovulation, if conception does not occur. In the days before contraception, once a woman started to be sexually active, it was likely that she would be pregnant or breastfeeding most of the time. Most women, therefore, had fewer than 30 periods in their lives, whereas the modern woman would expect to have 10 times that number during her reproductive life.

From menarche to menopause
From the time of onset of the first period (menarche), commonly occurring around age 12 (before nine is abnormally early and after 16 is abnormally late), the menstrual cycle continues (varying between 21 and 42 days in a normal woman) until the time of the menopause (climacteric).

When the ovaries cease to work in a woman's life, they do not produce an egg cell every four weeks, menstruation ceases and she is no longer able to bear children. The menopause can occur at any age between the middle thirties and the middle fifties - most commonly between 45 and 55.

The normal cycle
In the early part of the cycle, a hormone is produced (FSH - follicle stimulating hormone), in ever-increasing amounts by a pea-sized structure (the pituitary) in part of the brain stem. This leads to an increase in the oestrogen hormone being produced by the ovary, and with these changes the womb (uterus) lining is stimulated to grow.

Egg cells are also stimulated in the ovaries and on about Day 10 of the cycle one of these cells becomes dominant and takes over from all of the others. As the level of the oestrogen increases, another hormone is released from the pituitary gland to cause this dominant follicle - within which is the developing egg - in the ovary to rupture, releasing its ovum, the egg cell. This is ovulation.

The now collapsed follicle starts to produce (this remaining constant for 14 days) another hormone - progesterone - in the second half of the cycle, in order to encourage the womb lining to prepare itself for a fertilised ovum.

In the absence of pregnancy, both the oestrogen and the progesterone levels fall and this leads to the onset of menstruation, where the prepared lining is broken down and removed (the period, normally lasting four to seven days) and, once again, to an increase in the FSH with the start of another cycle.


Working out your ovulation
The relationship of ovulation to menstruation being relatively constant means that ovulation will only take place mid-cycle in a 28-day cycle. Using the first day of a menstrual period as Day 1, a 34-day cycle will have ovulation on Day 20, while a 42-day cycle will have ovulation on Day 28.

Ovulation is, therefore, always 14 days before the onset of the next period. When there is a varying length of menstrual cycle, this very normal function does make difficulties for couples trying to encourage conception by concentrating their efforts around the time of ovulation.

The fertile window
The most fertile time of the cycle has, traditionally, been said to be within a 24-hour period before and after ovulation. However, it has now been found that the 'fertile window' is probably much wider than was previously thought. In a significant number of women, it is often thought that ovulation can occur as much as three days before the usually supposed fertile window - and many women remain fertile well after Day 17.

Researchers have stated that variations not only occur between women, but they can also happen for individual women from cycle to cycle - this is perfectly normal. Some investigators have revealed that the probability of conception increases in the six-day period leading up to and including the day of ovulation. This fairly recent discovery probably accounts, in part, for the finding that some women seem to be more fertile than others.


Changes and variations
There are several variations, changes and abnormalities of the 'normal' menstrual cycle that can have varying effects and influences on a woman's life - especially as far as her fertility is concerned:

  1. 1. Amenorrhoea: the absence of the monthly menstrual cycle can be either primary or secondary. A significant delay in the time of the start of the first menstrual cycle is primary amenorrhoea. Delayed puberty is the commonest reason.

    Secondary amenorrhoea implies an absence of, or delay in, menstruation in a previously normal female and is most commonly due to pregnancy and breastfeeding. Menstruation re-appears after delivery or breastfeeding stops. Other causes are:

    • Severe weight loss (30 per cent)
    • Polycystic ovary disease (25 per cent)
    • Pituitary gland/hormone changes (30 per cent), most commonly as a result of a post-pill (oral contraceptives) effect.
    • Stress
    • Intensive exercise
    • Psychological factors - anxiety, depression or pseudocyesis (false sense of being pregnant).
    • Serious illness
    • Acute changes in the weather have also been reported as causing delay in the menstrual flow.

      • Natural menopause is said to be established, in retrospect, after there has been 12 months of amenorrhoea, in a non-pregnant woman over 35.

    • 2. Oligomenorrhoea is defined as sparse or infrequent menstruation, usually every three to six months. They can be long and irregular. Some of the above conditions can cause this, particularly polycystic ovary disease.
    • 3. Menorrhagia - excessively heavy, regular periods - may involve an excessive amount of blood loss, or normal blood loss with increased loss of tissue fluids. It may be associated with some form of organic disease in the uterus, or there may be menorrhagia in the absence of any detectable uterine abnormality, which is described as dysfunctional uterine bleeding (DUB).

      Few women talk in detail about their periods, so it is very difficult for them to know how the heaviness compares with anyone else. If a woman becomes anaemic and no other cause can be found, this may indicate that the periods are excessive. The other markers are whether there are clots forming and whether the woman experiences flooding. Other indications are tampons having to be changed every one to two hours, or double pads being used.

    • 4. Polymenorrhagia - frequent, heavy periods.
    • 5. Hypomenorrhoea - excessively light periods - but this is not a usual complaint.