Contraception: How Different Methods Prevent Pregnancy

Contraception includes medicines, devices, barriers and procedures used to reduce the chance of pregnancy. Effectiveness, safety, bleeding, convenience, fertility plans and infection protection all matter when choosing a method.

Pregnancy can be prevented at several points Pregnancy requires ovulation, viable sperm, fertilisation and implantation. Contraceptive methods interfere with one or more of these processes. Some methods prevent ovulation. Others block sperm, alter cervical mucus or create conditions that greatly reduce fertilisation. Several methods use more than one mechanism. Contraception prevents pregnancy from beginning. It does not end an established pregnancy. Choice should be voluntary and informed Contraceptive care should support informed choice rather than pressure someone towards one method. A clinician should explain effectiveness, expected bleeding changes, common side effects, important risks and how the method is used. The person's priorities matter. Someone may value lighter periods, no hormones, privacy, control or rapid return to fertility. Past experience also matters. A technically suitable method may still be unacceptable to the person considering it. Consent is required before any examination, injection, implant, intrauterine fitting or permanent procedure. Combined hormonal contraception Combined hormonal contraception contains an oestrogen and a progestogen. It includes the combined pill, contraceptive patch and vaginal ring. Its main action is suppressing ovulation. The brain and pituitary receive hormone signals that prevent the normal ovulation surge. Combined methods also thicken cervical mucus and change the uterine lining. These additional actions support contraceptive effectiveness, but suppression of ovulation is the main mechanism. Combined methods can make bleeding more predictable, lighter or less painful. They are not suitable for everyone because oestrogen increases the risk of blood clots and some arterial events. A clinician checks factors such as migraine with aura, smoking, age, blood pressure, clotting history and cardiovascular disease. Progestogen only contraception Progestogen only contraception includes several different methods: progestogen only pills, the implant, the injection and the hormonal intrauterine system. Progestogens thicken cervical mucus, making sperm movement through the cervix more difficult. The implant and injection usually suppress ovulation. Some progestogen only pills also suppress ovulation consistently. Other progestogen only pills mainly depend on cervical mucus and correct daily timing. Bleeding may become lighter, irregular, less frequent or absent. The pattern is not reliably predictable for one person. Irregular bleeding does not automatically mean the method has failed. The contraceptive implant The implant is a small flexible rod placed beneath the skin of the upper arm. It steadily releases a progestogen and usually suppresses ovulation. The implant is a long acting reversible contraception, or LARC, method. It works for several years without requiring daily action and is more than 99% effective. Its effectiveness can be reduced by some enzyme inducing medicines. The implant can be removed when pregnancy is wanted or when the user chooses to stop. The contraceptive injection The contraceptive injection releases a progestogen that suppresses ovulation. It is repeated at scheduled intervals, depending on the preparation. Periods may become irregular or stop. Weight, mood and other effects vary between users. The injection can temporarily reduce bone mineral density during use. Bone density usually recovers after stopping. Return to fertility can take longer after the injection than after most other reversible methods. This delay does not usually mean permanent infertility. The hormonal intrauterine system An intrauterine system, or IUS, is placed inside the uterus. It releases a small amount of progestogen, mainly acting within the uterus and cervix. It thickens cervical mucus and makes the uterine lining thinner. Ovulation often continues. The IUS is more than 99% effective and works for several years. Periods commonly become lighter, and some people eventually have little or no bleeding. The IUS can also be used to treat heavy menstrual bleeding, and a specific type and duration may be required when it provides the progestogen component of HRT. The copper intrauterine device An intrauterine device, or IUD, is a small device containing copper that is placed inside the uterus. It does not contain hormones. Copper creates conditions that impair sperm movement and function. This makes fertilisation very unlikely. The copper IUD is more than 99% effective and can remain in place for several years. Periods may become heavier, longer or more painful, particularly during the first months. The copper IUD can also be used as emergency contraception. Barrier methods A barrier method physically reduces the chance of sperm entering the uterus. External condoms are placed over the penis. Internal condoms are placed inside the vagina. Diaphragms and caps cover the cervix and are used with spermicide. Condoms reduce the risk of many sexually transmitted infections, called STIs. Other contraceptive methods do not provide the same STI protection. Condom effectiveness depends on correct use during every relevant sexual contact. Using an additional contraceptive method with condoms can provide both stronger pregnancy prevention and STI protection. Fertility awareness methods Fertility awareness methods use menstrual timing and physical fertility signs to estimate fertile days. Signs may include cycle dates, waking temperature and changes in cervical secretions. Users avoid vaginal intercourse or use a barrier method during the estimated fertile window. Effectiveness depends on careful daily observation, training and consistent action. Illness, irregular cycles, shift work and recent pregnancy can make interpretation harder. Apps that predict ovulation from dates alone may not provide a complete fertility awareness method. Withdrawal before ejaculation is less reliable and is not recommended as an effective contraceptive method. Permanent contraception Female sterilisation blocks or interrupts the fallopian tubes so sperm and egg cannot meet. Vasectomy interrupts the tubes carrying sperm from the testes. These procedures are intended to be permanent. Reversal is difficult, unavailable in many services and not guaranteed to work. Vasectomy is not effective immediately. Semen testing is needed before alternative contraception is stopped. Permanent contraception should follow careful, non coercive discussion of future reproductive choices. Perfect use and typical use Perfect use describes effectiveness when a method is used correctly every time. Typical use reflects missed pills, delayed injections, incorrect condom use and other real world variation. Methods requiring daily or event based action have a larger difference between perfect and typical use. LARC methods have similar perfect use and typical use effectiveness because the user does not need to remember them regularly. This does not make LARC the compulsory choice. Convenience and effectiveness must be balanced with preference and acceptability. Medicines and contraceptive effectiveness Some medicines increase liver enzymes that break down contraceptive hormones. These are called enzyme inducing medicines. They can reduce the effectiveness of combined hormonal methods, many progestogen only pills and the implant. Examples include some medicines used for epilepsy, tuberculosis and other conditions. The copper IUD and hormonal IUS are not generally affected in the same way. People should check before starting or stopping medicines, herbal products or contraception. St John's wort can also reduce the effectiveness of some hormonal methods. Health conditions affect method safety A method that is safe for one person may carry unacceptable risk for another. Combined hormonal contraception is usually unsuitable for people with migraine with aura. It may also be unsuitable after blood clots, stroke, significant cardiovascular disease or uncontrolled high blood pressure. Smoking becomes especially important when combined hormonal contraception is considered after age 35. Progestogen only or non hormonal options may be safer in several of these situations. However, every method has its own cautions. A clinician uses the complete symptoms and background rather than one rule. Contraception after pregnancy Ovulation can return before the first period following childbirth or pregnancy loss. Pregnancy can therefore occur before menstrual cycles appear to have restarted. Several methods can begin immediately or soon after pregnancy, depending on the method and clinical circumstances. Breastfeeding affects the timing and suitability of some options but is not a guarantee against pregnancy. Contraception during perimenopause Ovulation becomes less predictable during perimenopause, but pregnancy remains possible. Irregular periods alone do not confirm that contraception is no longer required. Hormonal contraception can also mask the natural menstrual pattern, making menopause harder to identify. Hormone replacement therapy is not contraception. The timing of stopping contraception depends on age, method and menstrual history and should be discussed clinically. Emergency contraception Emergency contraception reduces the chance of pregnancy after unprotected sex or contraceptive failure. The copper IUD is the most effective emergency method. It can usually be fitted within five days of unprotected sex, and it can remain in place as ongoing contraception when suitable. Levonorgestrel emergency contraception must be taken within 72 hours of sex. Ulipristal acetate can be taken within 120 hours. Emergency pills mainly work by delaying or preventing ovulation. They do not end an established pregnancy and are not abortion medicines. Emergency contraception is generally more effective when accessed promptly. The best option depends on timing, ovulation, other medicines, recent hormonal contraception and individual suitability. After emergency contraception An emergency pill does not protect against unprotected sex occurring later in the same cycle. The timing of restarting regular hormonal contraception differs between levonorgestrel and ulipristal acetate. Clinical or pharmacy advice is therefore important. A pregnancy test may be advised if the next period is late, unusually light or absent. Contraceptive failure does not imply blame No contraceptive method is completely fail proof. Pregnancy can occur through incorrect use, medicine interactions, vomiting, device expulsion or rare method failure. Care should focus on prompt options and informed decisions rather than blame.

Contraceptive methods prevent pregnancy through different mechanisms, so the safest and most acceptable choice depends on the individual.