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Introduction and history
Since ancient times, people have attempted to control the size of their families. Many methods of contraception are recorded. Most of the methods from history are barrier or withdrawal methods. The periodic abstinence method taught prior to the 1920s was imparted incorrectly. Soranus, a Greek gynecologist from approximately 200 CE, suggested that women should avoid intercourse during their menses because this was the time women were the most fertile. It was thought that the safest time for a woman was the midpoint of the menstrual cycle.[1] This teaching was overturned in the 1920s with the discovery that ovulation, in fact, occurs at the midpoint of the menstrual cycle. This then became one of the mechanisms of action to target in the development of more modern contraceptive methods.
It was not until 1960 that Enovid, the world’s first oral contraceptive pill (OCP) was released by G.D. Searle and Company. The pill was an instant success. After two years, 1.2 million American women were on the pill, and after five years, 6.5 million women were taking the pill, making it the most popular form of birth control in the United States. A current problem with the success of the pill is that modern women have the misconception that a monthly menstrual cycle is normal or needed. For most of human history, a significant portion of most women’s lives was spent either pregnant or lactating. Most women of reproductive age prior to the modern era likely had more months without periods than with periods.
Additionally, the number of maternal deaths averted by contraceptive use is high. Worldwide, it is estimated that without contraceptive use, the number of maternal deaths would be almost 266,000 higher per year than the current level. In terms of maternal mortality reduction, this is the equivalent of stating that contraceptive use reduced maternal mortality by almost 44%.[2]
Even with access to contraception, the problem of unintended pregnancy remains. In the United States, approximately half of unintended pregnancies are among women who were not using contraception at the time they became pregnant. However, the other half occurred among women who became pregnant despite reported use of contraception.[3] This is an important distinction and an opportunity to improve the consistent, correct use (CCU) of the chosen method.
How to measure contraceptive effectiveness
There are multiple methods of measuring the efficacy of a contraceptive. The “perfect use” failure rate expresses the number of unintended conceptions that occur when the individual uses the method consistently and correctly for one year. “Typical use” failure rate is the number of conceptions that occur when the individual routinely uses a method in an inconsistent or incorrect manner (i.e., missing medication/pills).
The Pearl Index (PI) is defined as the number of unintended pregnancies per 100 woman-years of method use. The PI is calculated by dividing the number of unintended pregnancies by the total number of woman months or exposure cycles of observation and multiplying by 1,200 (for months) or by 1,200 (for cycles). The PI may underestimate the contraceptive efficacy because it is often based on a lengthy exposure interval, usually one year. Because contraceptive failure rates decline with use, long study intervals may not reflect contraceptive efficacy associated with short-term use.
Contraceptive failure occurs in the first year of typical use for 9% of women using oral contraceptives, patch or ring; 18% of women relying on the male condom; 3% of women using injectable methods; and 24% using fertility awareness-based methods.[4] Failure rates of sterilization are comparable with those of long-acting reversible contraception methods such as intrauterine devices (IUDs) and the etonegestrel implant. The annual failure rates for the IUD are 0.8% for the copper T380A and 0.2% for the levonogestrel-releasing intrauterine system. The etonogestrel implant has a 0.05% reported failure rate, the lowest of any contraception method.
The U.S. Collaborative Review of Sterilization (CREST) was a prospective, multicenter observational study of 10,685 women conducted in 1996 by the Centers for Disease Control and Prevention (CDC) which showed that sterilization via laparoscopy or minilaparotomy is a highly effective method of contraception.[5] The risk of failure is substantially higher than the initial findings reported. The five-year cumulative failure rate of 13 per 1,000 for aggregated sterilization methods, compared with a five-year cumulative failure rate of 14 per 1,000 procedures for the copper T380A IUD. The five-year rate for the levonorgestrel-releasing IUD ranged from 5 to 11 per 1,000 procedures.[6]
The CREST study did not include Essure®. A summary of Essure experience reported two pregnancies in roughly 130,000 patients with microinsert hysteroscopic sterilization and bilateral occlusion confirmed by HSG (although both cases were the result of perforation/misplacement rather than device failure). If these data could be applied to the CREST data, Essure tubal occlusion with a confirmatory HSG would represent the most effective of all female or male sterilization techniques.[7]
Contraceptive method choice
Many elements should be considered when women, or couples, seek medical care for the purposes of contraception. Some of these elements include safety, effectiveness, availability (which includes accessibility and affordability), and acceptability.
Contraceptive method effectiveness is a critical element to consider, especially among women for whom an unintended pregnancy would pose additional health risks. Effectiveness involves two elements: the inherent effectiveness of the method itself and how it is consistently and correctly used. CCU can vary greatly with patient characteristics such as age, partner selection, income, motivation to prevent or delay pregnancy, and culture. Methods that depend on CCU by patients have a wide range of effectiveness between typical and perfect users. Given the data in the United States that approximately half of unintended pregnancies are among women who became pregnant despite reported use of contraception, there is an increasing trend toward IUDs and implants, which are long-acting reversible contraception (LARCs). These methods are highly effective because they do not depend on regular compliance from the user. LARCs are appropriate for most women, including adolescents and nulliparous women.
In choosing a method of contraception, the risk for HIV and other STDs should also be considered. LARCs and oral contraceptives (OCs) are highly effective at preventing pregnancy; however, they do not protect against STDs and HIV. CCU of the male latex condom reduces the risk for HIV infection and other STDs, including chlamydial infection, gonorrhea, and trichomoniasis.[8]
Availability (which includes accessibility and affordability) of any chosen method will be key to continued use of contraception. Funding of contraception is a public health issue that is worthy of debate.
Confirm nonpregnant state
When starting any form of contraception, a provider must be reasonably certain that the woman is not pregnant at time of initiation. As in other areas of medicine, a detailed history will usually provide the most accurate assessment of pregnancy risk for a woman who is going to initiate a contraceptive method. The following criteria have been found to be highly accurate (i.e., negative predictive value of 99%–100%) in ruling out a pregnancy among women who are not pregnant.[9] If a woman meets any one of the following criteria, then a health-care provider can be reasonably certain that she is not currently pregnant:
1. is ≤7 days after the start of normal menses
2. has not had sexual intercourse since the start of last normal menses
3. has been correctly and consistently using a reliable method of contraception
4. is ≤7 days after spontaneous or induced abortion
5. is within 4 weeks postpartum
6. is fully or nearly fully breastfeeding [exclusively breastfeeding or the vast majority (≥85%) of feeds are breastfeeds], amenorrheic, and <6 months postpartum.
If a woman does not meet any of these criteria, then the health-care provider cannot be reasonably certain that she is not pregnant, even with a negative pregnancy test. Routine pregnancy testing for every woman is not necessary prior to initiation of a contraception method. If a woman has had recent (i.e., within the last five days) unprotected intercourse, consider offering emergency contraception if pregnancy is not desired.
Reversible contraception
Barrier
Barrier methods such as the male and female condom, the diaphragm and cervical cap, as well as the contraceptive sponge, place a physical barrier between sperm and egg and thus prevent fertilization. Male and female sterilization also have the same mechanism of action, but are considered to be permanent.
The male condom is a barrier worn over the penis to prevent semen and sexually transmitted diseases (STDs) from coming into contact with a partner’s orifice (i.e., vagina, anus, mouth). Male condoms have been shown to decrease the transmission rate of HIV and other STDs. Step-by-step video instructions on proper condom use are available on the website of Planned Parenthood (www.ppfa.org). The concept of dual method is used to help prevent STDs. Condoms should be used at every sexual encounter, even if the couple is relying on another form of contraception. This additional contraceptive precaution is termed the use of dual methods. Although good in theory, many young women who are at greatest risk for STDs do not follow it.
The diaphragm is a latex rubber or silicone device designed to fit over the cervix and is used with a spermicide. The diaphragm keeps spermicide in close contact with the cervical mucus. Its mechanism of action is to function as a barrier to sperm, and the spermicide acts as a vaginal microbicide to kill sperm. Diaphragms are available only by prescription and must be individually fitted. There is variation between perfect use and typical use, secondary to user placement and motivation. Approximately 6–12 per 100 women per year will become pregnant with this method. The diaphragm must be worn for at least six hours after intercourse, but not more than 24 hours. It does not protect against STDs, and dual method male condom use is encouraged. It is an option for women who desire a nonhormonal method of contraception. Side effects, including increased incidence of urinary tract infections, are possible.
The Today Sponge®, a contraceptive sponge, debuted in the United States in 1983, and withdrawn in 1995 because of manufacturing deficiencies. Sales resumed in April 2005. The FDA never questioned the safety or efficacy of the Today Sponge. The device is moistened with two tablespoons of water and squeezed once. It is then placed high in the vagina covering the cervix. It must be inserted 30 minutes prior to intercourse and left in place for a minimum of 6 hours, and a maximum of 30 hours. One sponge is protective against repeated coital episodes during a 24-hour period. Prolonged sponge use is associated with vaginal infections and possible toxic shock syndrome. Perfect and typical use failure rates are 9% and 16%, respectively, for nulliparous women. In parous women, failure rates are increased to 20% and 32%, respectively. Concomitant male condom use is recommended to protect against STDs.
Hormonal
Oral contraceptive pills
Since the first birth control pill was released in 1960, women in the United States have made OCPs the most popular contraception method, with nearly 12 million US women and more than 100 million women worldwide taking OCPs. Combination OCPs contain estrogen and a progestin. Two estrogen formulations are commonly used. The predominant estrogen in low dose combination OCPs is ethinyl estradiol (EE). Mestranol, an estrogen found in older, high dose combination OCPs, is metabolized to EE. The first OCP Enovid-10 contained 150 μg mestranol and 9.85 mg norethylnodrel. Modern low dose combination OCPs contain between 20 μg and 50 μg of EE for their estrogen component.
The progestin formulation often varies. Combination OCPs are progestin dominant. The progestin is set to oppose the estrogen’s effect at the endometrium and prevent the luteinizing hormone (LH) surge in order to inhibit ovulation. There are presently more than 120 different brands of combination OCPs on the market in the United States. Some vary the amount of progesterone by week. Other formulations vary the number of pill-free days. Still others have an extended or continuous dosing.
The contraceptive failure rate for combination OCPs is approximately 0.3% in perfect use and 8.0% in typical use. Multiple variables can lead to decreased contraceptive efficacy, including side effects, general noncompliance (i.e., missing pills), increased body weight, and drug interactions. The side effects are often linked to early OCP discontinuation and subsequent contraceptive failure and unintended pregnancy. With the low dose OCP formulations, consistent timing of ingestion is an important factor in efficacy.
There are multiple contraindications to combination OCPs. Nearly all of the contraindications to combination OCPs are secondary to the pharmacologic level of estrogen. They include (1) prior history of thromboembolism, cerebrovascular disease, or coronary occlusion; (2) severely impaired liver function; (3) known or suspected breast cancer; (4) unexplained vaginal bleeding; (5) known or suspected pregnancy; (6) tobacco smoking in women >35 years; (7) severe hypercholesterolemia or hypertriglyceridemia; (8) uncontrolled hypertension; (9) migraine with aura. Full coverage of all contraindications is beyond the scope of this text; the American College of Obstetricians and Gynecologists (ACOG) has produced a practice bulletin that more completely addresses the use of hormonal contraception in women with coexisting medical conditions.[10] Additionally, the CDC has adapted the WHO recommendations for contraception use to give US Selected Practice Recommendations for Contraceptive Use, 2013.[11] A Google® search for CDC contraceptive guidelines will easily locate these documents free of charge.
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