7.6 - 7.7 - Contraception
Explain how hormonal and barrier contraception reduce the chance of pregnancy. Compare methods using evidence about effectiveness, user action, side effects and protection from sexually transmitted infections.
7.6 - Hormonal contraception changes the cycle
An ovary releases an egg at ovulation. For fertilisation, a sperm must reach that egg. Preventing egg release or blocking sperm passage therefore reduces the chance of fertilisation.
Hormonal contraception supplies hormones or hormone-like substances that change the menstrual cycle and reduce the chance of pregnancy. A progestogen may be natural or synthetic and has effects similar to progesterone; contraceptive methods use synthetic progestogens. Some methods contain both oestrogen and a progestogen, while others contain only a progestogen, so hormonal methods do not all work in exactly the same way.
At common tier, the key effects are:
- Oestrogen and progestogen in the combined pill prevent ovulation, so no egg is available for fertilisation.
- Progestogen can also thicken mucus at the cervix, making it harder for sperm to enter the uterus.
Higher extension: link to 7.5. FSH stimulates follicle and egg maturation, and an LH surge triggers ovulation. In the combined-pill feedback model, oestrogen and progestogen maintain inhibitory signals to the pituitary gland. Less FSH is released, so a follicle and its egg do not mature normally; less LH is released, so there is no LH surge and ovulation is prevented.
Both tiers: comparing hormonal methods
Some methods also make the uterus lining thinner. These additional effects vary by method, so it is inaccurate to say that every hormonal contraceptive contains both hormones or always prevents pregnancy in exactly the same way.
For example, an implant releases a progestogen, which can suppress ovulation and thicken cervical mucus.
Hormonal methods include daily pills, a weekly patch, a vaginal ring, an injection, an implant and an intrauterine system (IUS). Their delivery differs, but each uses hormonal control to reduce the chance of pregnancy. None protects against sexually transmitted infections (STIs).
Hormonal contraception prevents pregnancy before fertilisation: by preventing ovulation so there is no egg to fertilise, and in some methods by making sperm passage through the cervix more difficult.
7.7 - Evaluating contraception
To evaluate a method is to weigh evidence against the needs of the person using it. Useful criteria include pregnancy prevention under typical use, protection from STIs, frequency of action, reversibility, effects on periods, side effects and medical suitability. A method that is best by one criterion may be weaker by another.
| Method group | How pregnancy is prevented | Possible advantages | Possible limitations |
|---|---|---|---|
| Hormonal: for example pill, patch, injection or implant | Hormones can suppress follicle maturation or ovulation; some also thicken cervical mucus | Can be highly effective; long-acting methods need little regular user action; some methods make periods lighter or less painful | No STI protection; can alter bleeding and cause side effects; some methods are unsuitable for some people; pills depend on remembering doses |
| Barrier: external or internal condom | Physical barrier stops sperm meeting the egg | No hormonal effects; condoms also reduce the risk of STIs; used only when needed | Must be used correctly for each act of sex; can split, slip or be positioned incorrectly |
| Barrier: diaphragm or cap with spermicide | Covers the cervix, blocking sperm from entering the uterus | No hormonal effects; reusable | Correct positioning is essential; spermicide may irritate; does not protect against STIs |
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