Birth Control - Effectiveness

Effectiveness

Estimates of the effectiveness of a birth control method are generally expressed as the percentage of women who become pregnant using the method in the first year of use. Thus, if 100 women use a method that has a 0 percent first-year failure rate, then 0 of the women should become pregnant during the first year of use. This equals 0 pregnancies per 100 woman-years, an alternative unit. Sometimes the effectiveness is expressed in lifetime failure rate, more commonly among methods with high effectiveness, such as vasectomy after the appropriate negative semen analysis.

The most effective methods in typical use are those that do not depend upon regular user action. Surgical sterilization, Depo-Provera, implants, and intrauterine devices (IUDs) all have first-year failure rates of less than one percent for perfect use. In reality, however, perfect use may not be the case, but still, sterilization, implants, and IUDs also have typical failure rates under one percent. The typical failure rate of Depo-Provera is disagreed upon, with figures ranging from less than one percent up to three percent.

Other methods may be highly effective if used consistently and correctly, but can have typical use first-year failure rates that are considerably higher due to incorrect or ineffective usage by the user. Hormonal contraceptive pills, patches or rings, and the lactational amenorrhea method (LAM), if used strictly, can have first-year (or for LAM, first-6-month) failure rates of less than 1%. In one survey, typical use first-year failure rates of hormonal contraceptive pills (and by extrapolation, patches or rings) were as high as five percent per year.

Intrauterine devices (IUDs) were once associated with health risks, but most recent models of the IUD, including the ParaGard and Mirena, are both extremely safe and effective, and require very little maintenance.

Condoms and cervical barriers such as the diaphragm have similar typical use first-year failure rates (14 and 20 percent, respectively), but perfect usage of the condom is more effective (three percent first-year failure vs six percent) and condoms have the additional feature of helping to prevent the spread of sexually transmitted diseases such as HIV/AIDS.

The withdrawal method, if used consistently and correctly, has a first-year failure rate of four percent. Due to the difficulty of consistently using withdrawal correctly, it has a typical use first-year failure rate of 19 percent, and is not recommended by some medical professionals. Fertility awareness methods as a whole have typical use first-year failure rates as high as 25 percent per year; perfect use effectiveness depends on which system is used, perfect use failure rates are typically 3 to 9 percent, although for sympto-thermal methods the perfect use failure rate can be less than 1%. The evidence on which these estimates are based however is poor.

Family planning counselors should assess their client's needs and behaviors: "If exposure is likely, particularly to the more serious infections such as HIV, the one-method approach should be given greater weight. Conversely, in settings where unintended pregnancy is the greater concern, such as in many family planning clinics in developed countries, emphasizing the two-method approach as a first option may be appropriate." Although experts' opinions vary on this topic and some of them consider correct and consistent use of condoms as the most effective way of preventing pregnancy and STIs.

After stopping or removing many methods of birth control, including oral contraceptives, IUDs, implants and injections, the rate of pregnancy during the subsequent year is the same as for those who used no birth control.