Contraceptive efficacy: understanding how user and method characteristics play their part


Let’s face it. Contraceptive failure is the norm when measured over users’ reproductive life spans. The typical woman who uses reversible methods of contraception continuously from age 15 to age 45 would experience 1.8 contraceptive failures,[1] according to James Trussell and colleagues.[2] Of course, every provider knows that what matters most is correct and consistent use. But then again, technology fails people just as people fail technology. While we understand that women may not see contraceptive efficacy as their priority in selecting a method, they still need to have accurate information about efficacy. Unfortunately, provider bias often distorts the accuracy of what patients are told. And often, providers do not always include information on the factors that can make patients’ use of their chosen method more or less effective for them personally.

Make sure your staff provides consistent and correct information about contraceptive effectiveness.  One study of the information provided by family planning staff indicated that providers tended to give the lowest reported probabilities of pregnancy for pills and IUDs, probabilities of pregnancy during typical use for diaphragms and spermicides, and higher-than-typical probabilities of pregnancy for condoms.[3] (By the way, have you seen the updated probability figure for condoms? It has dropped to 13% from the previous 18%. More on that later.) Thus, family planning providers may extensively bias their patient education in favor of methods they provide most frequently. Condoms and withdrawal get an undeserved low efficacy score within many family planning clinics and offices. You can avoid unintentional bias by deciding carefully what pregnancy rates your clinic or staff members are going to use and by using visual aids, such as wall charts and handouts. See the chart at the end of this post for a helpful visual graphic designed by Trussell and colleagues.

Method Characteristics

Inherent Efficacy. Patients are sometimes told that unintended pregnancies are their own fault because they did not use their method correctly or carefully. However, contraceptive methods are imperfect and can fail even the most diligent user.

For some methods, such as permanent contraception, implants, and the levonorgestrel and the copper-T intrauterine devices (IUDs), the inherent efficacy is so high and correct and consistent use is so nearly guaranteed that extremely low pregnancy rates are found in all studies, and the range of reported pregnancy rates is quite narrow.

For other methods such as the pill and injectable, inherent efficacy is high, but there is still the potential inconsistent or incorrect use (e.g., forgetting to take pills or failure to return on time for injections), so that the characteristics of the user can contribute to a wider range of reported probabilities of pregnancy. In general, the studies of permanent contraception, injectable, implant, pill, patch, ring, and IUD use have been competently executed and analyzed. Studies of fertility awareness-based methods, spermicides, and the barrier methods display a wide range of reported probabilities of pregnancy because the potential for misuse is high, the inherent efficacy is relatively low, and the quality of the evidence is mixed.

User Characteristics   

Characteristics of the users can affect the pregnancy rate for any method under investigation, but the impact will be greatest for methods with the highest failure rates during typical use, either because the method has less inherent efficacy or because it is hard to use consistently or correctly.  The risk of pregnancy during either perfect or typical use of a method should remain constant over time for an individual with a specific partner, providing that underlying fecundity and frequency of intercourse do not change. It is possible, however, that the risk of pregnancy could decline during typical use of certain methods because the individual learns to use the method correctly and consistently. Which raises a question about the lowered probability figure for condom failure. Has our population of condom users become more consistent and more correct in its use? The stigma over condoms appears to have faded. Perhaps that along with more access to information and other factors has contributed to more successful use.

Imperfect use. The most important user characteristic is imperfect use of the method. For example, the 7% probability of pregnancy during the first year for typical use of the pill will not protect the careless user. The 17% probability of pregnancy during the first year of typical diaphragm use need not overly discourage a person who is a careful and methodical method user and who has infrequent intercourse from using a diaphragm.

The importance of perfect use is demonstrated in the few studies where the requisite information on quality of use was collected. For example, in a World Health Organization (WHO) study of the ovulation method, the proportion of women becoming pregnant among those who used the method perfectly during the first year was 3.1%, whereas the corresponding proportion failing during a year of imperfect use was 86.4%.[4] In a large clinical trial of the cervical cap conducted in Los Angeles, among the 5% of the sample who used the method perfectly, the fraction failing during the first year was 6.1%. Among the remaining 95% of the sample who at least on one occasion used the cap imperfectly, the first-year probability of pregnancy was nearly twice as high (11.9%).[5]

Frequency of intercourse. Among those who use a method consistently and correctly (perfect users), the most important user characteristic that determines the risk of pregnancy is frequency of intercourse. For example, in a study in which users were randomly assigned to either the diaphragm or the sponge, diaphragm users who had intercourse 4 or more times a week became pregnant in the first year twice as frequently as those who had intercourse fewer than 4 times a week.[6] In that clinical trial, among women who used the diaphragm at every act of intercourse, only 3.4% of those who had intercourse fewer than 3 times a week became pregnant in the first year, compared with 9.7% of those who had intercourse 3 or more times per week.[7]

Age. A female’s biological capacity to conceive and bear a child declines with age. The decline in ovarian reserve is moderate until a woman reaches her late thirties.[8] Risk of tubal factor infertility also increases with age among women who are exposed to STIs such as gonorrhea and chlamydia. Although many investigators have found that contraceptive failure rates decline with age,[9],[10],[11],[12] this effect almost surely overstates the pure age effect because age in many studies primarily captures the effect of coital frequency, which declines both with age and with marital duration.[13] User characteristics such as race and income seem to be less important determinants of contraceptive failure.


[1] Trussell J, Vaughan B. Contraceptive failure, method-related discontinuation and resumption of use: results from the 1995 National Survey of Family Growth. Fam Plann Perspect 1999;31:64–72, 93.

[2] Trussell J, Aiken ARA, Micks E, Guthrie KA. Efficacy, safety, and personal considerations. In: Hatcher RA, Nelson AL, Trussell J, Cwiak C, Cason P, Policar MS, Edelman A, Aiken ARA, Marrazzo J, Kowal D, eds. Contraceptive technology. 21st ed. New York, NY: Ayer Company Publishers, Inc., 2018.

[3] Trussell TJ, Faden R, Hatcher RA. Efficacy information in contraceptive counseling: those little white lies. Am J Public Health 1976;66:761–7.

[4] Trussell J, Grummer-Strawn L. Contraceptive failure of the ovulation method of periodic abstinence. Fam Plann Perspect 1990;22:65–75

[5] Richwald GA, Greenland S, Gerber MM, Potik R, Kersey L, Comas MA. Effectiveness of the cavity-rim cervical cap: results of a large clinical study. Obstet Gynecol 1989;74:143–8.

[6] McIntyre SL, Higgins JE. Parity and use-effectiveness with the contraceptive sponge. Am J Obstet Gynecol 1986;155:796–801.

[7] Frezieres RG, Walsh TL, Nelson AL, Clark VA, Coulson AH. Evaluation of the efficacy of a polyurethane condom: results from a randomized controlled clinical trial. Fam Plann Perspect 1999;31:81–7.

[8] Menken J, Trussell J, Larsen U. Age and infertility. Science 1986;233:1389–94.

[9] Grady WR, Hayward MD, Yagi J. Contraceptive failure in the United States: estimates from the 1982 National Survey of Family Growth. Fam Plann Perspect 1986;18:200–9.

[10] Grady WR, Hayward MD, Yagi J. Contraceptive failure in the United States: estimates from the 1982 National Survey of Family Growth. Fam Plann Perspect 1986;18:200–9.

[11] Sivin I, Schmidt F. Effectiveness of IUDs: a review. Contraception 1987;36:55–84.

[12] Vessey M, Lawless M, Yeates D. Efficacy of different contraceptive methods. Lancet 1982;1:841–2.

[13] Trussell J, Westoff CF. Contraceptive practice and trends in coital frequency. Fam Plann Perspect 1980;12:246–9.