The main raison d'etre for the development of once-a-month injectable contraceptives is the need for a long-acting method which produces a regular vaginal bleeding pattern. Although many women will successfully tolerate the amenorrhea or irregular bleeding which frequently accompany use of long-acting progestogen-only methods, there is a substantial minority, especially in certain ethnic groups, who find this unacceptable. The extensive literature does indicate that although combined estrogen-progestogen once-a-month injectables produce much more regular bleeding patterns than long-acting injectables like depot-medroxyprogesterone acetate, the patterns are not entirely normal. Detailed studies by the World Health Organization have demonstrated some deviation from normal menstrual patterns by users of the two once-a-month injectables, Cyclofem and Mesigyna. For example, 23.5% of Cyclofem and 25.2% of Mesigyna users experience irregular bleeding between 3 Cyclofem and 25.2% of Mesigyna users experience irregular bleeding between 3 to 6 months of use compared with 4.8% of untreated women, and 13.3% of cyclofem and 11.1% of Mesigyna users experience prolonged bleeding compared with 2.3% of untreated women. Comparable figures are much worse for DMPA users with a 35.7% incidence of irregular and 27.7% incidence of prolonged bleeding after similar duration of use. Bleeding patterns with all long-acting methods tend to improve with time. Overall group data for once-a-month injectable users are reasonably close to those of untreated women with, for example, a median of 15.6 days (5th and 95th percentiles: 7.5 and 26; confidence limits) of bleeding or spotting per 90-day reference period compared with a median of 18.5 days (5th and 95th percentiles: 12.2 and 25.5) for untreated women. Twelve-month life table discontinuation rates for menstrual bleeding disturbances are lower than expected for most progestogen-only met 2.1-5.2% for cyclofem and 0.8-4.2% for Mesigyna for amenorrhea, and 6.3-12.7% for cyclofem and 7.5-12.0% for Mesigyna for bleeding-related reasons. Once-a-month injectable contraceptives produce vaginal bleeding patterns much closer to normal than other injectables, but there are still significant deviations which lead to some discontinuation for-menstrual reasons. Hence, full explanation and counselling about possible menstrual changes are still essential for all intending users of these methods.
