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Injectable contraceptives combine almost complete effectiveness with reliable reversibility. Most clinical trials report less than 1 pregnancy per 100 women in the first year of use (39, 41, 271, 277, 336, 338, 340, 342). Thus injectables are comparable in effectiveness to Norplant implants, the TCu-380A IUD, and voluntary sterilization.

Women who have used DMPA or NET EN and stop to have a baby may have to wait several months longer on average for pregnancy than former IUD or OC users. Thus rumors persist that some women who use injectables become sterile. In fact, after two years pregnancy rates among former DMPA, IUD, and OC users are the same. Providers may need to reassure clients and the public that injectables do not cause infertility but to note that women should expect a wait of some months after stopping injectables to become pregnant. Service policies based on a fear of infertility--in particular, age and parity restrictions--can be dropped (see p. 24).

Effectiveness

Injectables work mainly by preventing ovulation. They suppress the surge in hormones from the pituitary gland that is necessary for ovulation (70). They also thicken cervical mucus, making it a barrier to sperm (357).

DMPA has been tested in a variety of doses and injection schedules. The 150 mg dose every three months (or 12 weeks or 90 days) is the most widely used regimen. The first-year failure rate in the US for the 150 mg dose is 0.3% compared with 0.4% for voluntary female sterilization, 0.4% for Norplant implants, 0.8% for the TCu-380A IUD, and 3.0% for oral contraceptives (370).

The 200 mg dose of NET EN is mostly used on a 2-month schedule. Some programs use a 2-month schedule for the first six months and then give injections every three months (107,193, 200, 209, 342). In a WHO trial the one year pregnancy rates for the two schedules were not significantly different: 0.4 per 100 women on the 2-month schedule and 0.6 on the 2-and then 3-month schedule. IPPF and WHO recommend the 2-month schedule, however (333, 365).

Monthly injectables also are highly effective (157, 166, 271, 331, 336). In a WHO trial there were two pregnancies among 1,152 Mesigyna users (0.2 per 100 women) and none among 1,168 Cyclofem users after one year (336). Women using Deladroxate, the precursor of many monthly injectables currently available through pharmacies in Latin America, had no pregnancies in 10 studies conducted in the 1960s and 1970s and covering more than 1,500 woman years of use (166).

The effectiveness of injectables depends on the timing of the first injection, adherence to the injection schedule, and the injection technique (see box, this page). In a Thai study the timing of the first injection made a significant difference in the accidental pregnancy rate. The 3-month pregnancy rate was 0.16 per 100 women receiving their first injection in the first eight days of the menstrual cycle but 0.62 per 100 women receiving their first injection after the eighth day (102). Thus the first injection is usually given during the first seven days of the menstrual cycle but can be given at other times (see Table 3).

The dosages and injection schedules ensure that users can come a little late for the next injection without risking pregnancy. As a guideline for programs, DMPA users can come at least two weeks late; NET EN users, at least one week late; and users of monthly injectables, up to three days late. if users come any later, the provider must be reasonably sure that they are not pregnant before giving the next injection. Clients also may return early (see Table 3).

[TABULAR DATA OMITTED]

Return to Fertility

Most former users of injectables can expect to become pregnant within a year after their last injection if they do not use another contraceptive. The largest study of return to fertility among users of DMPA, conducted in Thailand, found that women conceived nine months on average after the last injection, or 5.5 months after discontinuing, which the researchers assumed to be 15 weeks after the last injection (236). Other studies report similar findings (24, 277). By comparison, OC users in the Thai study conceived on average three months after discontinuing, and IUD users, 4.5 months after discontinuing (233, 235, 236) (see Figure 2). An Indian study found that 69 former NET EN users on the 2- and then 3-month schedule conceived on average 11 months after the last injection, or 8 months after they would have received their next injection. By comparison, 110 former IUD users in the study conceived on average about 3.5 months after discontinuing (21). With monthly injectables, studies of ovarian function indicate that most former users first ovulate three to four months after the last injection, or two to three months after the next injection would have been given (26, 27, 339).

Women have to wait to conceive partly because injectables remain in the bloodstream for several months after the next injection would have been given. DMPA, for example, is detectable in the bloodstream for eight months on average after one injection (277).

There is no evidence that injectables cause infertility. In the Thai study 91 % of former DMPA users had conceived within two years after discontinuing compared with 93% of former IUD users and 95% of former OC users. These differences are not statistically significant (236). By comparison, among US couples stopping contraception of all types, about 90% have conceived in 18 months, and about 1 0% of couples are infertile (351, 367). Amenorrhea may persist for several months after women discontinue injectables. Providers should warn women of this and reassure them that their regular cycles will return eventually.

Long-term users of injectables need not fear any cumulative impairment of fertility. There is no difference in the time to return of fertility between long-term and short-term users of DMPA (24, 87, 92, 235, 236, 277).

Despite this evidence, to avoid any possible blame for subsequent infertility, some programs have required women to have been pregnant at least once before allowing them to use DMPA. Such a policy restricts use unnecessarily. The McCormick Family Planning Program in Thailand followed this policy at first but removed it because of demand from women without children; indeed, some women lied about a previous pregnancy to be able to use DMPA. Following up these women after they stopped using DMPA, the program found no difference between their fertility and that of DMPA users who had had previous pregnancies (199).

RELATED ARTICLE: Injection Technique Important

Careful injection technique ensures that the full dose is absorbed at the right rate and thus is fully effective.

* With DMPA, providers need to shake vials to dissolve any sediment at the bottom, but they should not shake so vigorously that the liquid becomes frothy and difficult to draw into the syringe.

* With NET EN, warming vials to body temperature thins the viscous solution and makes it easier to draw completely into the syringe (333).

* With all injectables, the injection should be given in muscle because absorption may be too slow if the provider injects into fat (85). In contrast, massaging the injection site accelerates absorption and thus also should be avoided (333).