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Human sexual reproduction: 4. The use of hormones to control fertility - contraception to avoid pregnancy

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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 female fertility

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 e.g.

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 contraception.

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.

Progesterone also

(i) thins the lining of the uterus reducing the chances of a fertilised egg being implanted,

and (ii) prevents egg maturation - 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.

Progesterone-only pills (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 pressure.


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 progesterone.

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% effective.

(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 side effects:

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 irritation.

(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 to implant.

(iii) A copper IUD (non-hormonal) 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 non-hormonal contraception).

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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