Hormonal contraception prevents ovulation
Definition
Contraception
A method used to prevent pregnancy, either by using hormones or by stopping sperm reaching an egg.
- Contraception is the deliberate prevention of pregnancy.
- The combined pill contains artificial versions of oestrogen and progesterone.
- These hormones maintain feedback inhibition of the pituitary gland, so less FSH and LH are released.
- Without enough FSH, a follicle and its egg do not mature fully.
- Without an LH surge, ovulation does not occur, so there is no egg available for fertilisation.
Example
- The combined pill lowers FSH and LH release, so the follicle does not mature and the LH surge does not occur.
- No egg is released, so sperm cannot fertilise an egg and pregnancy is prevented.
Methods deliver hormones in different ways
Definition
Progesterone
A female sex hormone that maintains the lining of the uterus during the second half of the menstrual cycle and during pregnancy.
- Hormonal contraception can be delivered as a daily pill, skin patch, injection, implant or hormone-releasing intrauterine system.
- Long-acting methods release hormone over weeks, months or years, so their effect does not depend on remembering a tablet every day.
- A progesterone-only method mainly uses an artificial version of progesterone, while the combined pill supplies artificial oestrogen and progesterone.
- The exact pattern of bleeding can change because these methods alter the normal menstrual cycle.
Common Mistake
- Do not say the pill destroys an egg or stops an egg from existing.
- Write that it suppresses FSH and LH, preventing follicle maturation or ovulation.
Other effects also prevent pregnancy
- Artificial progesterone can thicken the mucus at the cervix, making it harder for sperm to enter the uterus.
- Some hormonal methods also keep the uterus lining thin, reducing the chance that an embryo implants.
- These effects support the main mechanism of preventing ovulation.
Exam technique
- For a two-mark explanation, give a mechanism and its consequence.
- For example, state that the cervical mucus thickens, then link this to sperm being less able to reach and fertilise an egg.
Hormonal methods do not prevent infections
- Hormonal contraception reduces the chance of pregnancy but does not form a physical barrier between partners.
- It therefore does not protect against sexually transmitted infections.
- A condom may be used as well when protection from sexually transmitted infections is needed.
Self review
- How do artificial oestrogen and progesterone reduce FSH and LH release?
- Why does suppressing the LH surge prevent pregnancy?
- How can thicker cervical mucus reduce the chance of fertilisation?
- Why does hormonal contraception not protect against sexually transmitted infections?
