tive pills (the first 21 of each 28-day cycle) without interruption. Oral contraceptive protection is expected to decrease when two or more consecutive hormonally active pills are skipped. 3 It is not uncommon for prolonged intervals to occur between doses of self-administered medication. 4 Between one-third and one-half of users of medications in pill form miss enough doses to place themselves at therapeutic risk at least occasionally. 5 Self-reports have shown that 3-60% of oral contraceptive

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... users, depending on the population studied, miss pills. 6 An increased risk of unintended pregnancy has been documented among women who have reported missing pills, 7 but this risk can be modified by two factors: the timing of coitus and the use of backup contraception. The instructions for correct oral contraceptive use that are included in all patient package inserts, which have the approval of the U. S. Food and Drug Administration, state that coitus should be avoided for the first seven days after initiating oral contraceptive use, whenever two or more consecutive active pills are missed and when the hormonefree week is extended by more than one day. D epending on their demographic characteristics, 3-27% of U. S. women using oral contraceptives become pregnant during their first 12 months of use. 1 The reasons for such large differentials are not known, but recent data show that women's use-related behaviors merit closer attention than they have so far received. 2 The risk of pregnancy is lowest for oral contraceptive users who use barrier protection any time they have coitus during the initial seven days of pill-taking and take all of the ac-during any of these intervals, an additional, backup contraceptive method (such as condoms) should be used until the woman has been taking hormonally active pills again for seven consecutive days. In this research note, we document the proportion of a sample of women who missed contraceptive pills during the first three months of use, as well as the proportions who were consistently protected against pregnancy by avoiding coitus or using backup contraception after missing pills. We also identify characteristics of women who were at increased risk of pregnancy during their first three months of oral contraceptive use. Methods In an earlier study, based on the same sample of women, we compared self-reports and electronic records of presumed pilltaking; details about the sample, methods of data collection and statistical tests are in the previous report. 8 Briefly, participants were 103 women initiating pill use (for the first time or after six or more months since last using the method) who were recruited from university student health services and Title X-funded clinics in Michigan and North Carolina in 1993-1994. Upon entering the study, the women completed a baseline questionnaire and received a free cycle of pills in a dispenser with an electronic monitoring device, as well as a monthly diary card on which they were asked to record a variety of information. The women were counseled to use condoms for any act of coitus during their first week of pill use and to use backup contraception for seven days if they missed two or more consecutive active pills. At the end of each of the first two pill cycles, the women completed another questionnaire and received the next free cycle of pills and a new diary card; they completed a final questionnaire at the end of the third cycle. The questionnaire provided demo-A three-month prospective study of 103 women initiating oral contraceptive use examined how consistently the women took their pills and whether those who missed pills employed other means to avoid pregnancy. The results showed that 52% took each active pill or never missed more than one pill at a time after the first week of the initial cycle, according to electronic devices that recorded the date and time each pill was removed from the blister pack. Another 21% were protected by behaviors that reduce the risk of pregnancy when two or more consecutive pills have been missed: avoiding coitus for the next seven days (18%) or using backup contraception during that period (3%). The remaining 27% were at increased risk of pregnancy. Predictors of increased risk were receiving low partner support for effective pill use, being unmarried and not considering it especially important to avoid pregnancy. Increased risk was most likely during the first seven days and during the third cycle of pill use.