Background
After initiating a new contraceptive method, the provider has little control of how or whether that method is used.
Objective
We sought to compare unintended pregnancy rates by the initial chosen contraceptive method after counseling to traditional contraceptive effectiveness in the same study population.
Study Design
The Contraceptive CHOICE Project provided reversible contraception to 9252 women at no cost during 2-3 years of follow-up. We performed 2 analyses of contraceptive efficacy in this prospective cohort: (1) intent-to-use (ITU), grouping participants based on their chosen method at enrollment; and (2) as-used, categorizing participant time according to the method used. In ITU analysis, switching of methods and method continuation were not considered, as we wanted to assess outcomes based on the method chosen at baseline. We used Cox proportional hazards models to compare rates of unintended pregnancy.
Results
During 20,017 person-years, we identified 615 unintended pregnancies. In ITU analysis, pregnancy rates were 5.3, 5.5, 2.0, 1.7, and 1.9 per 100 person-years for women initiating oral, injectable, implantable, copper, and hormonal intrauterine contraception (IUC) at baseline, respectively. The adjusted hazard ratio for injectable contraception compared to hormonal IUC was 2.4 (95% confidence interval, 1.8–3.3). Delaying initiation of IUC or implantable contraception increased unintended pregnancies by 60% (adjusted hazard ratio, 1.6; 95% confidence interval, 1.2–2.0). In as-used analysis, pregnancy rates were 6.7, 1.6, 0.2, 0.6, and 0.2 per 100 person-years for women using oral, injectable, implantable, copper, and hormonal IUC, respectively.
Conclusion
Although highly effective in the as-used analysis, women initially choosing injectable contraception had pregnancy rates similar to oral contraception and significantly worse than IUC or implantable contraception. Despite switching and discontinuation, women choosing an IUC or implantable contraception at baseline were much less likely to have an unintended pregnancy compared to those selecting other methods.
Introduction
In clinical practice, a medical professional can only directly influence the contraceptive method that an individual patient initiates at that particular visit. Many patients subsequently stop using the initial contraceptive method without consulting a medical professional or change to a less effective method. By examining unintended pregnancy rates by the method chosen initially, we are able to examine the combined effects of the effectiveness and continuation of that method. More practically, with an analysis of intended use, we can examine the results after a patient leaves the medical professional’s office with a new contraceptive method.
We are particularly interested in how injectable methods would perform in this analysis. Consensus has not been reached as to whether injectable contraception should be considered a long-acting reversible contraceptive (LARC) method. With perfect use, injectable contraceptives have contraceptive efficacy similar to intrauterine contraception (IUC) and implantable contraception, but in typical use, injectable contraception is more similar to oral contraception. Likewise, the continuation rate of injectable methods is more similar to oral contraception than IUC or implantable contraception. Internationally, LARC is defined as IUC and implantable contraception. However, the National Institute for Health and Care Excellence includes injectable contraceptive methods, such as depot medroxyprogesterone acetate (DMPA), as LARC.
The Contraceptive CHOICE Project was a longitudinal cohort study of 9256 women who were provided with no-cost, reversible contraception for 2-3 years. A prior analysis of contraceptive method use among CHOICE participants found that IUC and implantable contraception were 20 times more effective in preventing pregnancy during typical use than the contraceptive pill, patch, or ring. Women who were using DMPA were observed to have an unintended pregnancy rate that was similar to those using LARC methods. However, in that analysis women were only considered DMPA users if they received a DMPA injection in the past 3 months. Thus, the pregnancy risk for DMPA is closer to perfect use, and not comparable to the other methods reported.
To examine real-world use of all methods used in the CHOICE Project and to better quantify pregnancy risk of the contraceptive method a woman or girl begins, this analysis estimates the risk of unintended pregnancy based on the initial method choice of each participant. For the intent-to-use (ITU) analysis, we grouped women by the method they chose and initiated regardless of subsequent switching or discontinuation. We then compared the results of the ITU analysis to an updated analysis of the previously reported pregnancy rates based on traditional as-treated (termed “as-used” in this analysis) contraceptive effectiveness.
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