Compare barrier, hormonal, intrauterine and surgical methods, link each to the menstrual cycle, and know which also protect against sexually transmitted infections.
Contraception prevents pregnancy by stopping one of these steps: ovulation, sperm meeting the ovum (fertilisation), or the embryo implanting in the endometrium.
| Method | How it works | Protects against STIs? |
|---|---|---|
| Male or female condom | Barrier: stops sperm entering the uterus | Yes |
| Combined pill | Oestrogen and progesterone inhibit FSH and LH, so no follicle develops and no ovulation occurs | No |
| Injection / implant | Progesterone-like hormone stops ovulation and thickens cervical mucus | No |
| Intrauterine device (IUD) | Placed in the uterus; prevents fertilisation and implantation | No |
| Emergency contraception | High-dose hormone soon after intercourse delays ovulation | No |
| Tubal ligation | Oviducts cut, tied or blocked: ovum and sperm cannot meet (permanent) | No |
| Vasectomy | Sperm ducts (vas deferens) cut and tied: semen contains no sperm (permanent) | No |
FSH from the pituitary gland makes a follicle develop; a surge of LH triggers ovulation. Oestrogen and progesterone, at high levels, inhibit FSH and LH secretion (negative feedback). Hormonal contraceptives use this: keeping oestrogen and progesterone high prevents the FSH and LH needed for ovulation.
In a tubal ligation the oviducts are cut, tied or blocked. The ovaries still release ova and the menstrual cycle continues, but ova cannot reach the uterus and sperm cannot reach the ova. It is regarded as permanent, so doctors counsel people carefully, especially young people who may later want children.
Factors that affect the choice include effectiveness, side effects, whether the method is permanent or reversible, cost, cultural or religious views, and the need for STI protection. Dual protection — a condom plus another method — gives both high contraceptive effectiveness and protection against infections such as HIV.