New oral contraception study: pilot trial report Royal College of General Practitioners Manchester Research Unit.

In preparation for a large-scale cohort study of steroidal contraception 2 pilot studies involving 2400 members of the Royal College of General Practitioners have been carried out. The results obtained from these studies demonstrate the difficulties in selecting a suitable control population. The 1st study indicated that the prevalence of never-use of oral contraceptives (OCs) among sexually active women aged 16-29 years is only 5.1%. The prevalence of cigarette smoking was 20% among never-users compared to 37% among ever-users of OCs. The 2nd pilot study tested the acceptability of a new recruitment procedure involving recording of study subjects National Health Service number. 98% of patients understood and accepted this procedure. The mean age of this patient group was 22.5 years. 65% were single and 37% were cigarette smokers. 10% had had intercourse before the age of 16 years but only 4% had started using OCs before that age. Taken together these pilot studies confirm the non-feasibility of recruiting non-users of the pill as controls for a new steroidal contraception study. For each case physicians would have to interview an average of 29 women to find 1 age-matched control. Moreover never-users are not an appropriate comparison group since they differ in personal characteristics such as smoking habits. Although the absence of never-users will present problems in the interpretation of data from this study relationships to dose and duration of use can still be demonstrated. About 120000 women will need to be recruited to the study in order to assess the small changes in risk associated with low-dose OCs.