Question

Describe the principal methods of contraception, including their methods of action, likely failure rates, and protection against STDs.

Short answer

The principal methods of contraception are: 1. Barrier Methods: These prevent sperm from reaching and fertilizing an egg and have failure rates of 2-15%. They include male and female condoms and diaphragms. These methods provide protection against most STDs. 2. Hormonal Methods: These methods use hormones to prevent ovulation or alter the uterus environment, and have effectiveness rates of 91-99%. They include birth control pills, patches, injections, vaginal rings, and implants. They do not provide protection against STDs. 3. Intrauterine Devices (IUDs): These are small devices inserted into the uterus that have effectiveness rates of over 99%. They come in hormonal and copper forms and do not protect against STDs. 4. Emergency Contraception: Used after unprotected sex or contraceptive failure, these pills have effectiveness rates of 75-89% and do not protect against STDs. 5. Natural Methods: Fertility awareness techniques have effectiveness rates of 76-88% and rely on monitoring menstrual cycles, basal body temperature, and cervical mucus. They do not provide protection against STDs.

Step-by-step solution

1. Barrier Methods

Barrier methods of contraception work by preventing sperm from reaching and fertilizing an egg. They include male condoms, female condoms, and diaphragms. Male and female condoms are made of latex, polyurethane, or polyisoprene and provide around 85-98% effectiveness, with failure rates of 2-15%. Diaphragms are made of silicone and used with spermicide; they have a failure rate of approximately 12% when used correctly. Barrier methods are the only type of contraception that also provides protection against most STDs, including HIV. The protection level depends on the correct and consistent use of the barrier method during each sexual encounter.

2. Hormonal Methods

Hormonal methods of contraception involve the use of hormones to prevent ovulation, thicken cervical mucus (which makes it more difficult for sperm to reach the egg), or alter the lining of the uterus. These methods include birth control pills, patches, injections, vaginal rings, and implants. Their effectiveness rates range from 91-99%, depending on the method and consistency of use. The protection against STDs is non-existent for hormonal methods, so using a barrier method like condoms in combination is recommended for protection against STDs.

3. Intrauterine Devices (IUDs)

IUDs are small, T-shaped devices inserted into the uterus by a healthcare professional. There are two types of IUDs: hormonal and copper. Hormonal IUDs release progestin, which thickens cervical mucus and reduces the likelihood of sperm reaching the egg, while copper IUDs release copper ions that are toxic to sperm and impair their ability to fertilize an egg. IUDs have a low failure rate, with effectiveness rates of over 99%. They do not provide protection against STDs and should be used with barrier methods for optimal protection.

4. Emergency Contraception

Emergency contraception is used after unprotected sex or contraceptive failure (like a condom breaking) to prevent pregnancy. The two main types are emergency contraceptive pills (also known as "morning-after pills") and the copper IUD. The emergency contraceptive pills are either progestin-only (levonorgestrel) or a combined progestin-estrogen (ulipristal acetate) pill. The effectiveness of emergency pills ranges from 75-89%, depending on the type and how quickly it is taken after unprotected sex (within 72 hours for levonorgestrel and within 120 hours for ulipristal acetate). Emergency contraception does not provide protection against STDs.

5. Natural Methods

Natural methods of contraception involve tracking fertility signs such as menstrual cycles, basal body temperature, and cervical mucus to determine the fertile days, and either abstaining from sex or using barrier methods during those days. These methods have a varying degree of effectiveness, ranging from 76-88% based on different fertility awareness techniques, such as the Standard Days Method, the Sympto-Thermal Method, and the Cervical Mucus Method. Natural methods do not provide protection against STDs, and using barrier methods during fertile days is necessary for those who want to prevent the transmission of infections.