The main raison d'être 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 and 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 methods at 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.