The use of hormones to control
fertility - contraception to avoid pregnancy
Doc Brown's Biology exam study revision notes
There are various sections to work through, after 1 they can be read and studied in any order.
Sub-index of biology notes on human sexual reproduction
(4) Using hormones to control
How can hormones be used to control fertility?
In this case for contraceptive purposes.
There are several reasons for
reducing fertility leading to pregnancy by some method of contraception
The rising population of the
world - we must try to achieve sustainable populations - but there
are ethical issues here about controlling the freedom control the
size of family size a couple can have - a question of human rights.
Family planning to enable to
control when their children are born - a welcome lifestyle choice
for many people in the 21st century - can wait until they can afford
to raise a family.
Pregnancy can occur if a sperm
reaches an ovulated egg.
The idea of contraception is to
prevent pregnancy happening by one means or another.
Know and understand about the uses of hormones in controlling fertility.
Hormones are a key factor in
fertility, and can be used to decrease fertility - to decrease the
chance of pregnancy.
Oral contraceptive pills
You can take oral contraceptives that contain hormones
to inhibit FSH production so that no eggs mature. noting that .
Oestrogen is used to prevent
the release on an egg and the basis of one method of
Under normal circumstances in
the menstrual cycle, oestrogen stimulates the release of an egg,
BUT, if taken every day, keeping this hormone level high,
inhibits the production of FSH and after some time both egg
development and egg release are permanently stopped (as long as
oestrogen continues to be taken).
Progesterone also reduces
fertility by stimulating the production of thick cervical mucous,
preventing sperm getting through the entrance to the uterus (the
cervix) to reach an egg.
(i) thins the lining
of the uterus reducing the chances of a fertilised egg
and (ii) prevents egg
ovulation by inhibiting the production of FSH and LH
(this doesn't apply to some types of mini-pill).
Oral contraceptives eg 'the
combined contraceptive pill' may contain BOTH synthetic oestrogen and
progesterone to inhibit egg maturation ie prevent egg release, high and
sustained levels of oestrogen inhibit FSH production and egg development is
stopped permanently as long as the contraceptive is taken.
This 'pill' is sometimes
referred to as the 'combined oral contraceptive pill'.
It is taken as a cycle of 21
days of taking the pill daily, followed by no pill for 7 days.
This contraception method is
over 99% effective in preventing pregnancy.
However, there are side
effects e.g. headaches, nausea and it doesn't protect women from
sexually transmitted diseases.
In the first birth-control pills contained
too large amounts
of oestrogen which resulted in some women suffering
significant side effects eg headaches, nausea, irregular bleeding, fluid
retention and blood clots.
Birth-control pills now contain a much lower dose
of oestrogen, or only contain the hormone progesterone.
(e.g. the mini-pill oral contraceptive) lead to fewer side effects
and can be as effective as oestrogen pills.
This synthetic progesterone mini-pill must be
taken every day.
They are useful for older
women or women who can't take other contraceptive pills e.g. due
to some underlying medical condition such as high blood
Other hormone contraception
treatments - several formulations available
(a) The contraceptive patch
contains oestrogen and progesterone (same as combined pill).
It is usually 5 cm x 5 cm and is stuck on the skin and is 91-99% effective.
Typically, the patch is worn
on the skin in a 4 week cycle - its replaced once a week for 3
weeks and then no patch for 1 week.
(b) A contraceptive implant
is inserted under the skin and releases a continuous dose of
This stops the ovaries releasing an egg, it
thickens the cervix mucous, so hindering the sperm swimming to the
egg and so stops the implantation of a fertilised egg in the uterus.
A contraceptive implant can last for three years and is 99%
(c) A contraceptive injection
of only progesterone can have a effect for 2-3 months.
A few general comments
on hormonal methods of contraception (a) to (c)
Convenience - you don't
have to remember to take the pill every day, but you must
remember to change the patch or implant or receive the next
injection when appropriate.
High percentage of
effectiveness in preventing pregnancy.
Disadvantages - mainly
With any hormonal
contraceptive treatment you may get temporary side effects
at first, including headaches, nausea, breast tenderness, mood changes,
heavy and irregular periods.
The patch may cause skin
(d) An intrauterine methods
(IUD intrauterine device or IUS intrauterine system)
Intrauterine devices are T-shaped
and inserted into the uterus
to kill sperm which prevents the implanting of a fertilised egg.
There are two main types of
intrauterine methods, both of which are 99% effective.
(i) A plastic IUS
releasing progesterone into the womb (hormonal method as above and
can be effective for 3-5 years). The IUS prevents
fertilisation in two ways:
It thickens the
cervical mucus making it more difficult for the sperm to
move through the cervix.
It thins the
lining of the womb making it more difficult for an egg
(iii) A copper IUD
release traces of copper kills sperm, preventing them surviving in the uterus,
and so can never fertilise a released egg (non-hormonal
method, effective for 5 to 10 years.
Although not a hormonal method, as with
progesterone, the presence of copper:
It alters the cervical mucus, making it
more difficult for the sperm to reach and fertilise an
egg and survive.
It can also stop a fertilised egg
from being able to implant itself.
IUS and IUD contraception methods do not
protect against sexually transmitted infections.
See more in next section on other methods of
Keywords, phrases and learning objectives for this part on the use of hormones
to control fertility
Be able to describe the use of hormones to control
female fertility as a means of avoiding pregnancy using oral
contraceptive pill, injections, intrauterine contraception methods,
spermicide, plastic or copper IUD intrauterine devices (IUD and IUS)
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