More accurate information is provided by the life-table method. This method calculates the probability of pregnancy in successive months, which are then added over a given interval.
Problems relate to which pregnancies are counted: those occurring among all couples or those in women the investigators deem to have used the method correctly. Because of this complexity, rates of pregnancy with different methods are best calculated by reporting two different rates derived from multiple studies (i.e., the lowest rate and the usual rate), as shown in Table 10.2.
Safety Some contraceptive methods have associated health risks; areas of concern are listed in Table 10.3. All of the methods are safer than the alternative (pregnancy with birth), with the possible exception of estrogen-containing hormonal contraceptives (pills, patches and ring) used by women older than 35 years of age who smoke (6). Most methods provide noncontraceptive health benefits in addition to contraception. Oral contraceptives reduce the risk of ovarian and endometrial cancers and ectopic pregnancy. Barrier methods provide some protection against STDs including HIV, cervical cancer, and tubal infertility.
Table 10.2 Percentage of Women Experiencing a Contraceptive Failure During the First Year of Use and the Percentage Continuing Use at the End of the First Year
Women Experiencing Women Accidental Pregnancy within Continuing Use the First Year of Use (%) at 1 Year (%)
Combined pill and progestin-only pill 8 0.3 68
Patch (Evra™) 8 0.3 68
NuvaRing 8 0.3 68
ParaGard™(Copper T380A) 0.8 0.6 78
Myrena (levonorgestrel T) 0.1 0.1 81
DepoProvera 3 0.3 70
Lunelle 3 0.05 56
Norplanta and Norplant II 0.05 0.05 84
Implanon™ 0.05 0.05 84
Female sterilization 0.5 0.5 100
Male sterilization 0.15 0.10 100 aCumulative 5-year pregnancy rate for pliable tubing, divided by 5. From Hatcher RA, Trussell J, Stewart F, et al. Contraceptive technology. 18th ed. New York: Ardent Media, 2004:226, with permission.
present methods of contraception are assigned to one of four categories of suitability of use by women with more than 60 characteristics or conditions. The categories are: 1. A condition for which there is no restriction for the use of the contraceptive method; 2. A condition for which the advantages of using the method generally outweigh the theoretical or proven risks;
Table 10.3 Overview of Contraceptive Methods
HIV, human immunodeficiency virus; IUD, intrauterine device; PID, pelvic inﬂammatory disease; MI, myocardial infarction; DMPA, depomedroxyprogesterone acetate; STDs, sexually transmitted diseases.
3.
A condition for which the theoretical or proven risks usually outweigh the advantages of using method; 4.
A condition that represents an unacceptable health risk if the contraceptive method is used.
Cost Some methods, such as intrauterine devices (IUDs) and subdermal implants, require an initial high investment but provide prolonged protection for a low annual cost. A complex cost analysis based on the cost of the method plus the cost of pregnancy if the method fails concludes that sterilization and the long-acting methods are the least expensive over the long term (8) (Table 10.4).