If you're planning to get pregnant,
one thing that will really help you is having a good understanding
of the ovulation cycle.
Knowing the patterns of your own
ovulation cycle is key to ensuring that you have sex at the time
when you are most likely to fall pregnant.
You are most likely to fall pregnant
if you have intercourse in the day or two before ovulation occurs;
so an understanding of when that is likely to be, can help identify
your fertile period.
The ovulation cycle (also known as the
menstrual cycle) has four phases: menstruation, the follicular
phase, ovulation and the luteal phase.
Every woman's body goes through a
systematic process each month, where bleeding is followed by the
development and release of an egg, her uterus prepares for
impregnation, then either supports a pregnancy or breaks down the
uterine lining, and the ovulation cycle begins again with the first
day of menstruation.
The ovulation cycle operates a
biofeedback system, with hormones released in each phase also
influencing other glands to release different hormones, triggering
the next phase.
It all starts in the brain with the
hypothalamus, the core controller of the body's endocrine (gland)
system, which triggers the release of hormones, mainly oestrogen
and progesterone, from the pituitary gland, thus regulating the
ovulation cycle.
Length of Cycle
Although the 'average' menstrual cycle
is 28 days, women vary greatly. A'normal' cycle can be anything
from 21 to 35 days.
Most women's cycles tend to fall into
quite a regular pattern, although they can be disrupted, typically
by stress, illness or very high levels of physical activity.
However, the post-ovulation luteal
phase is thought to remain fairly consistent at between ten and 16
days in nearly all women, no matter how long their usual menstrual
cycle.
A study by Wilcox et al in 2000 in
North Carolina noted that the 'fertile window' can be very
unpredictable
Knowing that this phase is probably
going to be a certain number of days gives you the ability to start
charting your ovulation cycle and recognising the pattern.
Understanding the usual length of your
ovulation cycle allows you to count backwards, fourteen days, to
discover the time most likely to be your fertile period.
This can help understand your
ovulation cycle, particularly if you use some of the other signs
and signals to help you identify the time of ovulation more
accurately.
The ovulation cycle: first phase - menstruation
The ovulation cycle starts with the
first day of menstruation. Some women experience a time of spotting
before red blood appears. The appearance of red blood signals day
one of menstruation.
During menstruation, cells from the
lining of the uterus (or endometrium) are expelled through the
vagina along with blood and mucus.
The average time of bleeding can be
anything between three and seven days and the average blood loss
during menstruation is estimated at around 35 millilitres.
The ovulation cycle: second phase - follicular phase
Sometimes, descriptions of the
ovulation cycle combine the first and second phases (menstruation
and the follicular phase) into one, because the hormone levels that
trigger the onset of menstruation also trigger the very beginning
of the follicular phase.
The follicular phase is the period in
your ovulation cycle which begins with the production of follicle
stimulating hormone (FSH) and ends with
ovulation.
In the 'average' 28 day cycle, this
phase lasts until Day 14, however the length of this phase of the
ovulation cycle will vary greatly from person to person and even
from month to month, if your cycle is irregular.
Menstruation is triggered when a drop
in the level of the hormone progesterone at the end of the previous
ovulation cycle causes the uterus to start to shed its lining - and
this drop in progesterone also triggers the rise FSH.
A number of mature follicles in your
ovaries (between five and seven, according to some sources) each
start to develop an ovum (egg) ready for release from the
ovary.
Usually, just one egg will be released
(the release of more than one egg is not typical and is the reason
for non-identical multiple births). But in the lead-up to
ovulation, there is a race between the maturing follicles to become
the dominant one.
At the same time, the ovary also
starts releasing the hormone oestrogen, which triggers the
thickening of the uterine lining to prepare for the implantation of
a fertilised egg.
Rising oestrogen also changes the
make-up of cervical mucus, which becomes thinner and better able to
support sperm travelling towards the fallopian tubes to meet the
newly released egg.
By around Day 12 in an 'average'
cycle, one follicle will have established dominance and the other
follicles will start to degenerate.
The follicular phase ends when
oestrogen levels reach a peak, triggering the release of several
hormones (known collectively as gonadotrophins, these include
luteinising hormone, or LH).
The release of other hormones causes
the occurance of ovulation and also results in the levels of
oestrogen dipping. One hormone released, androgen, often promotes
an increase in sexual desire in women, clearly aimed at improving
your chance of getting pregnant.
The ovulation cycle: third phase - the ovulation event
The release of luteinising hormone
causes the mature follicle to release an egg within twelve
hours.
Around the same time, the release of
the hormone progesterone is likely to be the cause of a rise in
your resting body temperature shortly after ovulation.
Following ovulation, most eggs do not
live very long and unless they meet a sperm in the fallopian tube,
will leave the body.
If the egg has been fertilised, it
becomes a zygote; and that zygote then has several days to implant
into the now well-lined uterine wall. If these two events are
successful, you have a pregnancy.
Your body then enters the final phase
of the ovulation cycle, the luteal phase - and what happens next
depends on whether you are pregnant or not.
The ovulation cycle: fourth phase - the luteal phase
Following ovulation, the follicle that
released the egg keeps growing, becoming quite large in relation to
the size of the ovary, and transforms into something called the
'corpus luteum,' which is a temporary gland-like structure that
produces more hormones, particularly several oestrogens and
progesterone, which cause the levels of the hormones LH and FSH to drop and make the lining of the uterus
receptive to implantation of a zygote.
What happens next depends on whether
the egg has been fertilised or not.
If you are pregnant, implantation
causes the production of the hormone human chorionic gonadotropin
(hCG), which enables the corpus luteum to continue to produce
progesterone for several weeks until the placenta has developed
sufficiently to take over this role. The corpus luteum then
degrades into the surface of the ovary.
If there is no pregnancy, the corpus
luteum starts to degrade straight away due to the low levels of LH
and FSH and it stops producing
progesterone and oestrogen. As levels of these hormones drop, the
ovulation cycle begins again as the uterus sheds its lining and the
production of FSH is triggered.
The ovulation cycle and the moon
There's no evidence-based research
showing a link between a woman's menstrual cycle and the phases of
the moon, although the average menstrual cycle is around the same
length of time as a lunar cycle.
Many scientists argue that this is
coincidental. There has been some suggestion that the pineal gland
(which secretes melatonin) is influenced by changes in light and
darkness and may play a role in regulating hormones, and studies in
the 1970s by Dewan found that light could influence ovulation
regularity.
But there is absolutely no scientific
evidence to support a theory that women experience two fertile
times during one ovulation cycle because of a "natal lunar phase"
and it is wise to be wary of claims that encourage you to purchase
further information about this.
By Fran Molloy, journalist and mum
of four