Biology 7.6 - 7.8 - Contraception and fertility
Explain how hormonal and barrier methods reduce pregnancy risk and compare their advantages. Higher-tier work applies reproductive hormone control to clomifene therapy and IVF.
Hormonal contraception
Contraception reduces the chance of pregnancy. Hormonal contraception contains synthetic hormones that act like natural oestrogen or progesterone; the synthetic form of progesterone is called progestogen.
Hormonal methods change the normal hormone signals of the menstrual cycle. They provide signals that suppress the normal stimulation needed for an egg to mature and be released. In methods such as the combined pill and the implant, the main effect is that ovulation usually does not occur. With no egg released, sperm cannot fertilise an egg, so pregnancy is prevented.
Progestogen can also make the mucus at the cervix thicker, making it harder for sperm to pass into the uterus. Some hormonal methods also make the uterus lining thinner. The balance of these effects depends on the method, so it is inaccurate to claim that every hormonal contraceptive works in exactly the same way.
Two examples show different ways to deliver hormones:
- The combined pill contains oestrogen and progestogen and must be taken regularly.
- The contraceptive implant releases progestogen over several years and does not depend on remembering a tablet each day.
Hormonal contraception can prevent pregnancy, but it does not protect against sexually transmitted infections (STIs).
Comparing contraception
Barrier method
A contraceptive method that physically prevents sperm from reaching an egg.
External and internal condoms are barrier methods. A condom keeps semen and sperm from entering the vagina or uterus when it is used correctly. A diaphragm or cap is placed over the cervix to block sperm, usually with spermicide. Condoms can also reduce the transmission of many STIs; a diaphragm or cap does not provide that STI protection.
Typical use includes mistakes such as missing a pill or a condom coming off. Perfect use means the method is used correctly every time. The current NHS figures below describe pregnancy prevention over one year, not the chance from one act of sex.
| Method | Type and main action | Typical use | Perfect use | Useful advantages | Important limitations |
|---|---|---|---|---|---|
| Contraceptive implant | Hormonal; usually stops ovulation | over 99% | over 99% | long acting; no daily action | requires fitting/removal; can change bleeding; no STI protection |
| Combined pill | Hormonal; usually stops ovulation | 91% | over 99% | reversible; can make periods more regular, lighter or less painful | daily action; possible side effects; not suitable for everyone; no STI protection |
| External condom | Barrier; prevents sperm entering the vagina | 82% | 98% | no hormones; used only when needed; reduces STI transmission | must be used correctly every time; can split or come off |
Source for effectiveness figures: NHS, How well contraception works at preventing pregnancy, checked 17 September 2026.
There is no single method that is best for everyone. A valid evaluation matches evidence to a person's priorities: effectiveness in typical use, STI protection, how often action is needed, reversibility, possible side effects, and medical suitability. For example, an implant may better suit someone who wants a highly effective method that needs no daily action, while condoms add STI protection that the implant does not provide.
When comparing two percentages, subtract to find a difference in percentage points. For example, 98% minus 82% is 16 percentage points. This differs from a relative percentage increase, which would divide the change by the starting percentage before multiplying by 100. These data describe groups over one year and cannot predict one person's outcome.
Hormones in assisted reproduction
Higher tier only
Assisted Reproductive Technology (ART) uses medical treatment to help fertilisation or pregnancy. Hormone control can be used in two different ways: to restart ovulation using clomifene therapy, or to control the production and collection of eggs for in vitro fertilisation (IVF).
Clomifene therapy
Clomifene is a medicine, not a hormone. It reduces the oestrogen feedback signal detected by the brain and pituitary gland. The pituitary therefore releases more FSH and LH: FSH stimulates follicle and egg maturation, and LH can trigger ovulation. This can help a person who does not ovulate regularly.
In vitro fertilisation (IVF)
In vitro means outside the body, in laboratory conditions. A simplified IVF sequence is:
- Fertility hormones with FSH-like action stimulate several ovarian follicles so that several eggs mature. More mature eggs means more eggs can be collected and may form embryos; it does not guarantee pregnancy.
- The follicles are monitored and a trigger hormone is used to time final egg maturation. The eggs are then collected from the ovaries.
- Eggs are mixed with sperm in a laboratory. If fertilisation occurs, early embryos begin to develop.
- A selected embryo is transferred to the uterus. Hormone medication can help prepare and support the uterus lining.
Only fertilisation and early embryo development happen in the laboratory. The embryo must be transferred to the uterus for a pregnancy to continue. Treatment is medically monitored because stimulating several follicles can cause side effects and because success is not guaranteed.