In other words, do our beliefs about clinically important bleeding patterns reflect women’s beliefs?
TABLE 1
The WHO Belsey system of bleeding patterns
| Pattern | Definition |
|---|---|
| Amenorrhea | No bleeding |
| Prolonged bleeding | 1 or more bleeding-spotting episodes lasting longer than 14 days |
| Frequent bleeding | More than 5 bleeding-spotting episodes |
| Infrequent bleeding | 1 or 2 bleeding-spotting episodes |
| Irregular bleeding | 3 to 5 episodes with more than 3 bleeding-free intervals of 14 days or longer |
| Normal bleeding | None of the above are present |
| This system establishes criteria for defining clinically important bleeding patterns during a 90-day reference period. Adapted from: Belsey EM et al.4 | |
Implantable contraception
The etonogestrel (ENG) implant (Implanon) is the only implantable contraceptive available in the United States. This single-rod contraceptive can be used for as long as 3 years.
Contraceptive implants, including the levonorgestrel implants once sold in the United States and still available in some parts of the world, are highly effective. The Implanon prescribing information reports a first-year failure rate of 0.38 pregnancies for every 100 woman-years of use; Hatcher and co-workers reported a failure rate of 0.5 The difference is based on how the FDA defines pregnancy in contraceptive trials. In fact, the only pregnancies reported with the ENG implant happened after it was removed. Importantly, the studies evaluated by the FDA included only women not using any medications known to induce liver metabolism (the cytochrome P450 pathway) and who were between 80% and 130% of ideal body weight. The efficacy of the ENG implant for women who are taking medications that induce liver metabolism or who are greater than 130% of their ideal body weight is unknown.
The efficacy of the ENG implant is likely derived from suppression of ovulation and increased cervical mucus viscosity. Associated changes in the endometrium that occur with this low dosage of progestin are likely the primary cause of irregular and unpredictable bleeding.
Several studies have sought to describe the bleeding patterns experienced with the ENG implant.6-8 During the first 3 months, approximately 50% of all women using the ENG implant reported bleeding-spotting (TABLE 2) for 30 days, on average (TABLE 3). The number of days decreases to approximately 20 bleeding-spotting days for each 90-day reference period at 6 to 24 months, with wide variability. For example: From 3 to 6 months, women reported 22 days of bleeding-spotting (standard deviation, 20 days); from months 21 to 24, 20 days of bleeding-spotting (standard deviation, 14 days).7
After using the ENG implant for 2 years, therefore, most women can expect the number of bleeding-spotting days for every 90-day reference period to range between 6 and 34 days. These days of bleeding-spotting are often noncontinuous, however. On average, women reported three separate bleeding-spotting episodes for every 90-day reference period.7
Although individual bleeding patterns are unpredictable, women who had no bleeding, or infrequent bleeding, at the beginning of use of the ENG implant had only a “small chance” of bleeding frequently.6 The most common bleeding pattern observed throughout the study was infrequent bleeding, defined as fewer than three episodes of bleeding in a 90-day reference period (excluding amenorrhea).7
Amenorrhea may not persist. The amenorrhea rate at 6 months of use and beyond ranges from 10% to 20% (TABLE 4). Importantly, women who are amenorrheic in one 90-day reference period are not necessarily the ones who are amenorrheic in another reference period. So, unlike what is more commonly seen with other progestin-only methods, such as injectables, amenorrhea is not sustained for most women.
This unpredictable pattern affects continuation of the ENG implant (TABLE 5). Irregular bleeding is the most common reason women cite for discontinuation, accounting for 30% to 60% of all women who discontinue early.7,9
Overall, approximately 4% of ENG users discontinue the method at 1 year. Ten percent to 20% discontinue each year thereafter because of intolerance to bleeding changes.6-9
There are, however, differences in discontinuation rates across cultures. In an integrated analysis of 13 different trials that evaluated patterns of vaginal bleeding with the ENG implant where the rate of menstrual changes was similar, women from Europe and Canada were much more likely (23%) to discontinue the implant because of those changes than women from Southeast Asia and Chile were (2%).6 This finding may reflect differences in cultural beliefs or disparate access to other contraceptive options.10
TABLE 2
What percentage of women taking progestin-only contraception report bleeding-spotting?
| Months | ||||||
|---|---|---|---|---|---|---|
| Study | 3 | 6 | 9 | 12 | 18 | 24 |
| DMPA | ||||||
| Sangi-Haghpeykar (1996)33 | 46% | 43% | 40% | |||
| Cromer (1998)34 | 24% | 10% | ||||
| ENG implant | ||||||
| Croxatto (2000)9 | 40–50% | |||||
| LNG-IUS | ||||||
| Datey (1995)32 | 18% | 6% | 3% | 1% | 4% | |
| Hidalgo (2002)20 | 25% | 8% | 11% | |||
| Progestin-only pill | ||||||
| Sheth (1982)35 | 21–55%* | 6–42%* | ||||
| * Percentage reporting prolonged, frequent, or irregular bleeding. | ||||||
| Key: DMPA, depot medroxyprogesterone acetate; ENG implant, etonogestrel implant; LNG-IUS, levonorgestrel intrauterine system. | ||||||
TABLE 3
How many days of bleeding-spotting do women have
when they use progestin-only contraception?