The menstrual cycle from menarche to menopause

Menstruation has many names (period, monthly cycle, the flow) but, whatever you call it, it is the term given to cyclical monthly bleeding from the uterus of adolescent girls and pre-menopausal women. This regular discharge of blood, tissue, fluid and mucous usually lasts 3 - 6 days.

The start: Menarche is the name given to the first menstrual period, which usually occurs between the ages of 11 and 16.

The end: Menopause is that point in time when periods stop permanently. It is also called the "change of life" or "climacteric".

The cause

Hormones are the boss of this process. During the menstrual cycle, female sex hormones - oestrogen and progesterone - prepare the uterus to support a pregnancy. If pregnancy does not occur, the endometrial lining which coats the uterus sloughs off producing the menstrual flow.

The process

  • When an adolescent girl – the average age of onset is between 11 and 16 years – or woman ovulates, a mature egg (one that can be fertilised) is released by one of her two ovaries.
  • If, as it travels along the Fallopian tubes, it is met by sperm, the egg is fertilised and pregnancy may occur. This fertilised egg will then adhere to the lining (endometrium) of the uterus, producing a hormone (BetaHCG) which prevents menstruation by stimulating the ovary to continue producing progesterone and the pregnancy will proceed.
  • However, if there is no fertilisation the endometrium comes away from the uterine wall. This occurs 14 days after ovulation and is due to the falling progresterone levels. The lining disintegrates and passes through the vagina as menstrual flow.

The average cycle

A menstrualcycle normally lasts 28 days: it starts on the first day of a period and ends on the first day of the next period.

However, the duration of menstrual cycles vary, especially during menarche and perimenopause (the years leading up to menopause).

  • Day 1 of bleeding is referred to as Day 1 of the menstrual cycle. This is when the thickened lining (endometrium) starts to shed.
  • Ovulation occurs, on average, on Day 14 of a 28-day cycle. This is when a mature egg is released to travel down the Fallopian tube. The lining of the uterus (endometrium) has thickened in preparation. If no conception occurs, the lining and blood sheds: this is menstruation.

Flow varies with the heaviest loss usually during the first two or three days. The total amount of fluid, in a normal period, averages about 80ml or small teacup.

The menstrual cycle can be divided into the following parts: the ovarian cycle and the uterine cycle.

Ovarian cycle

The ovarian cycle involves changes in the ovaries:

Phase 1

The follicular phase (days 1 -13) is from the first day of menstruation until ovulation. Maturation of the egg initially takes place inside the follicle in the ovary. Ovulation occurs around day 14 and this is your most fertile period.

Phase 2

The luteal phase (days 14 through 28) starts on ovulation day and lasts until the first day of menstruation. The luteal phase has a more precise timeline and usually is only 12-16 days from the day of ovulation. This ultimately means that the day of ovulation will determine how long your cycle is.

  • If the egg is fertilised by sperm and attaches to the endometrium, a pregnancy begins. (This pregnancy is dated from Day 1 of this menstrual cycle.)
  • If the egg is not fertilised or does not attach, the endometrium begins to break down and the menstrual cycle starts again.

It is not uncommon – or abnormal – to have a short cycle of about 21 days or a longer one of 35 days. Anything outside those limits should be discussed with your medical practitioner.

Problem periods

Many women battle with PMS or premenstrual syndrome which usually starts a few days before the onset of a period and disappears as soon as it starts.

Some women bleed a profuse amount: this is called menorrhagia. Others fail to menstruate: amenorrhoea. Some women have debilitating, unrelenting cramps: dysmenorrhea.

And then there are those who suffer from chronic pain caused by endometriosis which occurs when endometrial tissue has planted itself outside of the uterus. Oligomenorrhea is a scanty menstrual flow, when the interval between periods exceeds 35 days but is not long enough to qualify as amenorrhoea. Most women with oligomenorrhoea also have cycles in which no eggs are released. Oligomenorrhoea can progress to amenorrhoea.

Reviewed by Dr Andrew Newham MBChB (UCT) FCOG (SA)

(Robyn von Geusau, Health24, February 2011)

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