so what I've sketched out here is a
typical ovarian cycle also called a
menstrual cycle and this cycle goes from
day one to day 28 and in the middle we
have day 14 and we're going to start off
by considering an idealized menstrual
cycle so how do we know when the
menstrual cycle begins well that's quite
easy because we have the onset of
menstruation on the first day of the
menstrual cycle and that will go on for
the first five to seven days of the
menstrual cycle as the endometrium form
the previous month is discharged or the
inner lining of the endometrium form the
previous month is discharged through the
vagina so day one is the day that
menstruation is first noted and then of
course the end of the menstrual cycle
will be when the menstruation occurs
again at the start of the next menstrual
cycle so that will be day 28 now
ovulation classically occurs on day 14
of the menstrual cycle so the ovum will
release or the ovum will be released
from the ovary on day 14 of the
idealized menstrual cycle
now it's interesting that sperm can live
inside the female genital tract for a
perhaps up to five days so that was day
seven there that would be day nine then
sperm can live for up to five days in
the female genital tract and certainly
they can readily live for up to three
days that will takes up to day eleven
so sperm can live for up to five days
and certainly easily live for three days
and remain in very viable numbers when
you're discussing this it depends
whether you're wanting to optimize
conception or to minimize conception
let's think about first of all
minimizing conception so to minimize
conception obviously sexual intercourse
shouldn't take place during this period
of time this would be the Fertile period
and in addition to that the ovum can
last for about 24 hours once it's been
released 12 to 24 hours so in theory the
period where the conception could occur
is if sexual intercourse in sexual
intercourse occurs between day 9 and day
15 if only it were this simple now of
course menstrual cycles are knocked
consistently 28 days with ovulation
occurring occurring exactly on day 14
now it's true that the second half of
the menstrual cycle day 14 today 28 does
tend to be fairly consistent so that
means that if a menstrual cycle lasted
for 30 days as it could well and the
last half of the menstrual cycle was
indeed 14 days then in that 30-day
menstrual cycle ovulation would have
occurred on day 16 but of course we
don't know that till the end of the
month or the start of the next cycle
conversely the menstrual cycle one month
could be 26 days and given that it's the
second half of the menstrual cycle that
tends to be consistent if it was a 26
day menstrual cycle that means in that
cycle ovulation will have occurred on
day 12 which of course pushes everything
back and of course we don't know that
until the next menstrual period comes
along and menstrual cycles can vary
really quite dramatically so to use this
as a means of contraception it is is a
complete non-starter
is not a safe viable means of
contraception and if you're a health
care professional or of a teacher teach
young people this that even as
experienced clinicians we're not really
smart enough to work out when the safe
period is so certainly and then
professionals are not going to be able
to do that because we can't do it so we
can't use this as as a means of
contraception it does say when
fertilization is more likely to occur or
less likely to occur but we can never
know so as a means of contraception we
do not teach this but of course people
want to conceive sometimes so to
maximize the probability of conception
what sort of advice should we give
people
well if ovulation occurs on day 14 and
the sperm remain very viable inside the
female genital tract for three days
then I think you can see that anything
from day 11 and the ovum are going to
live the ovum lives for 12 to 24 hours
after it's been produced I think you can
see that the time when conception is
most likely to occur is if sexual
intercourse occurs from day 11 to day 14
point five that's the time that
conception is most likely to occur and
it's probable that conception is most
likely to occur if the sperm are already
waiting high in the fallopian tube so
the sperm would be deposited high in the
vagina the spoon will have to travel
through the cervix through the uterus up
into the fallopian tube because
conception occurs high in the fallopian
tube what we should call the uterine
tube actually bad habit we should now
call it the uterine tube now the sperm
probably take between well we don't
really know actually probably between an
hour and 12 hours to be able to swim up
into the high fallopian tube but
sometimes that can be aided by active
muscular
tractions of the cervix and the uterus
but still the best time is going to be
in that period when conception is most
likely to occur now how do we know when
this time is going to be to advise
couples on the best of chances of
conceiving in a particular ovarian cycle
well of course if the cycles are regular
at the regular 28 days then ovulation is
very likely to be on day 14 but of
course we can't guarantee that because
the first half of the menstrual cycle
particularly has a variable time course
so there's a bit of it's a bit of
probability here a bit of what you might
call look involved so some women are
aware of a sensation that they can
associate with ovulation and if that
were the case and they were to have
intercourse very shortly after that then
it's reasonable that the sperm could get
up into the fallopian tube in that first
12 to 24 hours and and lead to
conception that's certainly viable many
women don't have a physical sensation
though associated with ovulation
sometimes in the days before ovulation
the temperature will go down a little
bit and then the temperature will rise a
little bit not much more than half a
degree centigrade if I'm not even that
point two or point three over to URI
centigrade so there can be a slight blip
in temperature associated with ovulation
that can be observed for with accurate
recordings of temperature and round
about the time of ovulation and just
before ovulation there's a change in the
nature of the the mucus that there's
abundant clear stretchy cervical mucus
produced to facilitate the passage of
sperm around about this time as well so
sometimes we can educate women to
recognize the changes in their mucous
and thereby indicating at which time
sexual intercourse will be most likely
to generate a conception now all this
process is controlled by the the brain
actually by the
the hypothalamus producing
gonadotrophins or moans and that will
affect the pituitary gland and the
pituitary gland will produce follicular
stimulating hormone which will stimulate
the follicle to start developing the
first half of the menstrual cycle
causing the follicle to produce
estrogens from the granulosa cells and
then in the second half of the menstrual
cycle this is going to be controlled
largely by the luteinizing hormone from
the pituitary gland from the anterior
lobe of the pituitary gland which is
going to stimulate the production of
estrogen but lots of progesterone
is produced in the second half of the
menstrual cycle so East region is
largely stimulating the development of
the endometrium progesterone is
maintaining the development of the
endometrium in the second half of the
menstrual cycle and then when the levels
of estrogen and progesterone start to
drop towards the end of the cycle the
endometrium is no longer maintained
they'll be very very constriction in the
endometrium and menstruation will occur
so just a little bit there about the the
practical aspects of the the ovarian or
the menstrual cycle