Table : table 42.1 Methods of Contraception

Method	Mode of action	Failure rate^a	Comments
Unprotected	No form of birth control.	85	High risk of pregnancy, especially for women 15–30.
Nontechnological methods
Rhythm method	The couple abstains from intercourse between days 10 and 20 of the ovarian cycle (peak fertility).	15–35	High failure rate due to miscalculation and/or variation of individual cycles.
Coitus interruptus	The man withdraws his penis prior to ejaculation with the intention of not depositing sperm into the vagina.	20–40	Requires self-control, especially by the man. Very high failure rate.
Barrier methods^b
Condom (male or female)	A sheath of impermeable material (often latex) is fitted over the erect penis or into the vagina. Semen is trapped in the condom, so no sperm are deposited in the vagina.	3–20	If fitted correctly, an intact condom can prevent pregnancy. Failure can be due to material failure or improper use. Condoms are the only contraceptive method that protects against sexually transmitted diseases (STDs), including HIV (AIDS).
Spermicidal jellies	Applied deep inside the vagina, these chemical compounds kill or immobilize sperm.	25	Used alone, spermicidal compounds have a high failure rate.
Diaphragms, cervical caps, cervical sponges containing spermacide	Inserted by the woman prior to intercourse, these devices work by blocking the cervix so that sperm cannot pass into the uterus.	15–30	Approximately the same failure rate as condom use by men, but do not protect against STDs. Can be used in conjunction with spermicidal jelly for extra protection.
Hormone-based contraceptives
Oral hormones (“the pill”)	A daily pill for women containing a combination of synthetic estrogens and progesterone. These hormones mimic pregnancy to the extent that the ovarian cycle and ovulation are suspended. The uterine cycle can continue by including a week of non-hormone administration every 21–28 days.	0–3	Requires medical consultation and prescription. Taken correctly, oral contraceptives are extremely effective. In the United States, more than 12 million women use them each year; they are sometimes prescribed to treat menstrual disorders.
Non-orally administered hormones	Making use of same hormonal actions as the pill, these methods include long-acting injections, patches that release hormones transdermally (through the skin), and a hormone-containing vaginal ring. Implantable progestin releasing have a failure rate of <1 and can last up to 3 years.	<5	Same as oral hormones. A slightly lower failure rate because the woman does not have to remember to take a daily pill.
Progestin-only pill (Plan B^b)	An oral contraceptive meant to be taken within 72 hours after unprotected sex. A high dose of progestin in two pills prevents ovulation in the same manner birth control pills do.	5–40	Not an “abortion pill,” this drug will not terminate an existing pregnancy. Currently available to women over 17 without a prescription. Failure rate varies widely depending on when taken.
Implantation blockers
Intrauterine device (IUD)	A medical professional inserts a small plastic or metal device into the uterus. The resulting inflammation reaction (see Chapter 40) releases prostaglandins, which prevent implantation of the fertilized egg.	<1	A highly effective contraceptive, it is the most widely used birth control device in China (and hence the world). With medical monitoring, can remain in place for several years.
Contragestational pill	Mifepristone or RU-486 is a drug that blocks the action of progesterone that is necessary to maintain the endometrium during implantation and pregnancy.	0.5–6	Prevents implantation when taken up to several days after unprotected intercourse. Can terminate a pregnancy up to the time of the first missed menstrual period. In the United States, available from specialized providers.
Sterilization
Vasectomy	The vasa deferentia (see Figure 42.8) are cut and tied off so that sperm can no longer pass into the urethra. Sperm continue to be produced but are reabsorbed by the man’s body. Male hormone levels and sexual responses are not affected.	0–0.15	A simple surgical procedure performed under local anesthetic in a doctor’s office. Although theoretically it can be reversed, vasectomy should be considered permanent.
Tubal ligation	The oviducts (see Figure 42.11A) are tied off so that eggs cannot reach the uterus and sperm cannot reach the egg. As with vasectomy, hormone levels and sexual responses are not affected.	0–0.05	This surgical procedure is somewhat more complex than vasectomy. It is often performed in conjunction with childbirth when a woman has decided that her family is complete.
^aFailure rate refers to the number of pregnancies per 100 women per year. ^bAll of these barrier methods are routinely available without medical prescription.