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The risk of pregnancy without contraception is 2–4% for each unprotected act of intercourse. In 100 women using no contraception, 85 pregnancies occur per year. Approximately half of all pregnancies in the developed world are unplanned and many of these women report using some form of reversible birth control at the time they became pregnant. Only absolute abstinence completely prevents pregnancy. While no form of contraception is perfect in sexually active women, helping patients to choose a contraceptive method that they are able to use consistently and correctly can decrease unintended pregnancy (Fig. 25.1). With perfect use, oral contraceptives (OC) are nearly as effective as long-acting reversible contraceptives (LARC), such as the intrauterine device (IUD), progesterone intramuscular injection and progesterone implants. However, with typical use, LARC methods are approximately 10 times more effective.

“Natural” family planning
Natural family planning or fertility awareness aims to avoid conception by abstention from intercourse during the woman’s fertile period. It makes use of a calendar and some indicator of ovulation (basal body temperature measurements, cervical mucus characteristics or commercial ovulation prediction kits). Intercourse is avoided during the so-called fertile period at ovulation and for several days before and after. Natural family planning requires a highly motivated couple, regular menstrual cycles and the willingness to tolerate a failure rate of up to 25%. The method has no medical side effects and is accepted by virtually all religions.

Barrier methods
There are three general categories of barrier contraception: condom, diaphragm and cervical cap. All work by preventing spermatozoa from entering the woman’s uterus and fertilizing an egg. Barrier methods are good choices for individuals who want to limit contraceptive efficacy to a particular sexual episode. They are readily reversible and can be used in conjunction with the timing methods associated with natural family planning. The most serious side effects of barrier methods occur in individuals with an unknown latex allergy.
Condoms that fit over the penis are more widely available than condoms that fit inside the vagina (the female condom). Male condoms may be made from latex rubber, polyurethane or animal intestines; each provides a different “feel” or sensitivity for the man during intercourse. Female condoms are typically made of polyurethane. Intact condoms stop sperm and infectious agents from entering the vagina and so can prevent transmission of HIV and other sexually transmitted diseases. They must be carefully removed after ejaculation to avoid spilling semen from the condom into the vagina. The failure rates of condoms are 3–6% with perfect use and 15% with typical use. The diaphragm is a soft latex or plastic dome that fits inside the vagina and covers the cervix. Because some sperm may be able to bypass the diaphragm and gain access to the uterus, spermicide is placed in the dome of the diaphragm. Diaphragms are individually fitted by a clinician and require some training for proper insertion and removal. A diaphragm should be left in place for 6–8 h after inter course, and additional spermicide placed into the vagina if more episodes of intercourse occur before it is removed. Diaphragms partially protect against HIV and other sexually transmitted diseases. Some women develop bladder or vaginal infections during diaphragm use. The failure rate of a properly fitted diaphragm with perfect use is about 6%; it rises to 15% with typical use.
Cervical caps are similar to, but smaller than, the diaphragm. They are individually fitted to tightly cover the cervix. Failure rates are similar to those of the diaphragm. Cervical caps are not widely available.

These are chemicals that kill sperm by disrupting their outer cell membranes. The most commonly used are nonoxynol-9 and octoxynol-9. Spermicides are available suspended in one of three vehicles: foam, jelly or wax suppositories. Spermacides are recommended for use with a barrier method, because the failure rate of spermicide used alone is up to 30%. There are few absolute contraindications to their use. They have an unpleasant taste and can cause an allergy in some users. Spermicide use may cause inflammation of the female genital tract and has been associated with an increase in the transmission of sexually transmitted infections, including HIV.

Intrauterine devices
The IUD is a small T-shaped device, placed into the uterine cavity and attached to a monofilament thread that hangs into the vagina, allowing the user to confirm that it remains in place. The modern IUD provides safe, long-acting, highly effective and rapidly reversible contraception with few side effects. The precise contraceptive mechanism of the IUD is not known, but it is thought to work by preventing fertilization as well as causing the endometrium to be inhospitable for implantation. The 10–12 year copper IUD produces a local inflammatory response in the endometrium and excess prostaglandin production. The copper ion competitively inhibits a number of zinc-requiring processes in sperm activation and endometrium/ embryo signaling. The 3- and 5+-year progestin-releasing IUDs thickens cervical mucus, creating a barrier to sperm penetration into the upper genital tract. Additionally, the progestin disrupts the normal proliferative- to-secretory sequence of endometrial maturation.
Historically, IUDs, such as the Dalkon Shield, were associated with increased risk for medical complications and reproductive damage among users who were infected with sexually transmitted pathogens. This increased risk was likely due to the braided IUD tail, which allowed bacteria to ascend into the upper genital tract. The monofilament string, used on all modern IUDs, does not have this risk. In women at high risk for sexually transmitted infections (STIs), screening should be performed prior to IUD insertion. Women should be advised to use a barrier method for prevention of HIV and other STIs. Side effects of the copper IUD include increased menstrual bleeding, iron-deficiency anemia and dysmenorrhea. The progestin IUD reduces menstrual flow and may be used to treat menorrhagia and adenomyosis. The IUD is highly effective, with a failure rate <1% per year. If pregnancy occurs, it is more likely to be ectopic in location. However, compared with women using no form of contraception, women with IUDs still have a reduced risk of ectopic pregnancy.

Hormonal contraception
Combination oral contraceptive pills (often called OCPs) are the most widely used form of hormonal contraception. They include a synthetic estrogen (ethinyl estradiol or mestranol) combined with a variety of synthetic progestins and are typically taken orally for 21 consecutive days of every 28 and allow monthly withdrawal bleeding. The progestin component of combination OCPs varies in its activity on progesterone receptors, androgen receptors and mineralocorticoid receptors. The estrogen and progestin dosages in monthly combination OCPs may be constant over the 21 days or may be sequentially modulated (phased or triphasic pills). Some newer combination oral contraceptive regimens provide continuous rather than monthly exogenous hormone cycles, often allowing endometrial sloughing only 3-4 times per year. Combination OCPs prevent pregnancy by multiple mechanisms, including inhibition of ovulation, thickening of cervical mucus to prevent sperm transport and alteration of the uterine lining to block implantation.
OCPs have benefits beyond pregnancy prevention, including decreased risk of pelvic inflammatory disease (PID), benign breast disease, anemia and endometrial and ovarian cancer. They are not totally risk free, however, and are associated with increased risk of thromboembolic disease, nonthrombotic stroke and gallbladder disease. Women over 35 who smoke should not use combination OCPs. Failure rates are <1% with perfect use and about 8% with typical use. To be effective, OCPs must be taken in the correct order on a daily basis.
Combinations of estrogen and progestin are also available for contraception in nonoral formulations. These include transdermal patches, injections and vaginal rings. All have efficacy similar to combination OCPs, and may have reduced metabolic side effect profiles.
Progestin-only contraceptives can be administered orally, by intramuscular injection or as a subdermal implant. All work by thickening cervical mucus and altering the endometrial lining of the uterus. The oral form of the progestin-only contraceptive, often called the mini- pill, is useful in women with contraindications to estrogen such as breastfeeding or high thrombotic risk. With perfect use, the mini-pill has a failure rate comparable with OCPs. However, the half-life of the mini-pill is short, with nearly undetectable plasma levels at 24 h. Thus, to maximize effectiveness, the mini-pill requires precise compliance with all 28 active pills taken at the same time daily.
Depo-medroxyprogesterone acetate (DMPA) is a progestin contraceptive given as an intramuscular injection every 12–14 weeks. Common side effects include irregular bleeding, particularly in the first 6 months of use, and weight gain. Because of the length of action of DMPA, side effects may persist until the medication is cleared and return to fertility may be delayed.
The original six-capsule subdermal levonorgestrel progestin implant (Norplant) has been replaced with an equivalent two-capsule system (Jadelle, 5 years of use), and a single capsule subdermal etonorgestrel implant (Implanon, 3 years of use). Insertion and removal are generally quick and uncomplicated, but must be performed by a trained clinician. Side effects include irregularly irregular vaginal bleeding.
Hormonal emergency contraception can be effective in preventing pregnancy if taken within the given time interval after unprotected intercourse or a contraceptive failure. Plan B, consisting of 1.5 mg levonorgestral, prevents pregnancy using the same mechanisms as other progestin contraceptives if taken within 120 h of exposure. Combination estrogen progestin  emergency contraception  may  also  be used up to 120 h following exposure; however, the combined hormonal regimen has more side effects and a lower effectiveness than the progestin-only regimen. The copper IUD may also be used for emergency contraception up to 5 days after unprotected intercourse.

Sterilization of both men and women are surgical methods of permanent contraception. Sterilization prevents the gametes from reaching the point of fertilization.
In women, sterilization is commonly performed by laparoscopic tubal ligation. Tubal ligation interrupts the fallopian tubes and may involve the use of tying, blockade, cautery, partial excision or banding. Ten-year cumulative failure rates for female sterilization are 0.75– 3.5%, depending upon the method. If a pregnancy does occur after tubal ligation, up to 50% are in an ectopic (tubal) location because of the blockage of the fallopian tube. Transcervical sterilization involves placement of micro-inserts into the fallopian tubes using a hysteroscope. This method requires no incision and can be performed in a doctor’s office. Disadvantages include the need to wait 3 months for tubal occlusion to occur and confirmation of occlusion using a radiographic dye test called a hysterosalpingogram. Failure rates appear similar to laparoscopic methods.
The sterilization procedure used in men is called a vasectomy. It involves bilateral interruption of the vas deferens as they leave the testes in the scrotum. Surgical methods for interruption include partial excision, cautery or tying. Vasectomy is typically 100% effective but requires a 3-month waiting period and multiple postprocedure ejaculations to clear the vas deferens of previously produced sperm.