Contraceptive Efficacy Definition
Contraceptive efficacy is measured as the percentage of women experiencing an unintended pregnancy during the first year of use of a contraceptive method, making the correct answer B. 1
Standard Measurement Framework
Contraceptive effectiveness is consistently reported using a one-year timeframe across all methods, regardless of the method's intended duration of use. 1
- The measurement represents the number of pregnancies that will occur in 100 women each year using that method 1
- This standardized annual measurement allows for direct comparison between different contraceptive methods 1
- The timeframe is always the first year of use, not the total duration of the method's effectiveness 1
Two Categories of Effectiveness
Contraceptive efficacy is reported in two distinct categories to capture real-world performance: 1
Perfect Use
- Represents pregnancies occurring when the method is used perfectly (both consistently and correctly) 1
- Reflects the inherent efficacy of the contraceptive method itself 1
- For example, combined oral contraceptive pills have a perfect use failure rate of 0.3% per year 1
Typical Use
- Represents pregnancies occurring with typical use, which includes inconsistent or incorrect use 1
- Reflects real-world effectiveness accounting for human error and adherence issues 1
- For example, combined oral contraceptive pills have a typical use failure rate of 8-9% per year 1
Clinical Application
Methods that depend on consistent and correct use have a wide range of effectiveness between perfect and typical use. 1
- Long-acting reversible contraceptives (LARCs) like IUDs and implants show minimal difference between perfect and typical use because they are not user-dependent 1
- User-dependent methods like oral contraceptive pills show substantial differences: 0.3% perfect use versus 8-9% typical use 1
- For women with conditions where unintended pregnancy presents an unacceptable health risk, long-acting highly effective methods should be prioritized over barrier methods or behavior-based methods due to their lower typical-use failure rates 1
Common Pitfall
Do not confuse the measurement timeframe with the duration of method use. 1
- A method like Nexplanon (effective for 3 years) or Mirena IUD (effective for 8 years) still has its efficacy reported as pregnancies per 100 women per year, not over the entire duration of use 1
- This standardization enables clinicians to compare a 3-month injectable with a 10-year IUD on equal footing 1