Contraception

How hormonal contraception works

The menstrual cycle is normally coordinated by FSH, LH, oestrogen and progesterone. Hormonal contraceptives artificially alter this control system. The administered hormones maintain signals that reduce the release of FSH and LH. Consequently, an egg is less likely to mature and the LH surge and ovulation are prevented.

The combined oral contraceptive pill contains oestrogen and a progesterone-like hormone. Progesterone-only methods can also inhibit ovulation and thicken the mucus at the cervix, making it harder for sperm to enter the uterus. Hormones may be delivered by a pill, skin patch, injection, implant or hormonal intrauterine system (IUS). An implant, injection or IUS does not depend on remembering a tablet every day, so it can be more reliable in everyday use.

Hormonal methods can be highly effective and some can make periods lighter or more regular. However, they may cause unwanted effects such as headaches, nausea, acne or mood changes. The nature and likelihood of side effects vary between people and methods. Some require fitting or administration by a healthcare professional. Crucially, hormonal contraception does not reduce the risk of sexually transmitted infections.

Non-hormonal methods

Barrier methods physically stop sperm reaching an egg. Condoms are worn during sexual intercourse; diaphragms are placed over the cervix and are often used with spermicide. These methods avoid hormonal side effects. Condoms also reduce the risk of transmitting many STIs, although they must be used correctly every time and can tear or slip. A diaphragm must be positioned correctly and left in place for the required time after intercourse.

A copper intrauterine device (IUD) is fitted inside the uterus. It releases copper ions that impair sperm, making fertilisation very unlikely. It is highly effective, long-lasting and requires little action once fitted, but fitting requires a trained professional and it can cause heavier or more painful periods in some people.

Fertility-awareness methods involve identifying the fertile part of the menstrual cycle and avoiding sexual intercourse, or using a barrier method, at that time. They use no drugs or devices, but ovulation cannot always be predicted accurately. Illness, stress and natural variation can alter the cycle, so careful and consistent monitoring is needed. They do not protect against STIs.

Sterilisation is intended to be permanent. In a vasectomy, the sperm ducts are cut or sealed so sperm do not enter the semen. In female sterilisation, the oviducts are cut or blocked so sperm and egg cannot meet. These procedures are very effective and require no action during intercourse, but involve surgery, may very rarely fail and should not be treated as readily reversible. They do not protect against STIs.

Evaluating a contraceptive method

There is no single best method for everyone. A sound evaluation considers:

• effectiveness: how well it prevents pregnancy;
• dependence on the user: whether it must be remembered daily or used correctly every time;
• duration and reversibility: whether it is short-term, long-acting or intended to be permanent;
• health effects: possible side effects, medical risks and whether surgery or professional fitting is needed;
• STI protection: condoms reduce transmission risk, whereas hormonal methods, IUDs, fertility awareness and sterilisation do not;
• practical and personal factors: convenience, acceptability, access and plans for future pregnancy.

Effectiveness figures must also be interpreted carefully. “Perfect use” assumes that instructions are followed every time; “typical use” includes missed pills, incorrect use and other mistakes. A long-acting method may therefore suit somebody who finds daily contraception difficult, while condoms remain important where STI transmission is a concern. Using a condom alongside another contraceptive can address both concerns.

An evaluative conclusion should follow from the stated situation. For example, a highly effective implant may suit someone wanting reversible, long-term contraception without daily action, but it would not replace a condom when protection from STIs is also needed.