Sexual and reproductive life events in relation to duration of oral contraceptive use.

In order to disclose differences between users and non-users of oral contraceptives (OC), 620 women aged 15-54 were invited to participate in an in depth interview about sexual, contraceptive, and reproductive life events. Of the 585 women who participated, 459 were consecutive gynecological in- or outpatients, and 126 were selected from visitors in general practice. Data was analysed by multivariate test statistics. After correction for present age and social class, the duration of use of OC (DOC) among women 15-34 years of age correlated negatively to age at menarche and coital debut and positively to number of sexual partners, oral-genital sexual practice, and number of pelvic inflammatory diseases. Among women over 35, DOC was positively associated only to cigarette smoking. No correlation was found to coital frequency (whether earlier, present or during pregnancy or menstruation), number of births and abortions, or to social classification. In epidemiological research on benefits and risks of oral contraceptives, confounding influence of one or more variables is of crucial importance. The present findings point at sexual and life-style habits as potential confounders in the study of OC and associated diseases.