The prescription of oral contraceptives and its relation to the incidence of chlamydia and abortion in Sweden 1997–2005

Aims: The aim of this study is to examine the association between the prescription of oral contraceptives and the incidence of chlamydia, and between the prescription of oral contraceptives and the number of abortions in a population-based ecological study. Methods: For this study we used register data from the Swedish Institute for Infectious Disease Control (chlamydia incidence), the Swedish National Board of Health and Welfare (number of abortions), Statistics Sweden (population data), and Apoteket (Swedish pharmacy) (prescriptions for oral contraceptives). We conducted ordinary least squares regression analysis of the association between chlamydia or abortions and the prescription of oral contraceptives. Results: The prescription of oral contraceptives has a positive association on both the incidence of chlamydia and the numbers of abortion. Our best model predicts that prescription of 100 yearly doses of oral contraceptives increase the abortions by 3.3 cases among 16-year-old women and 0.7 cases among 29-year-old women, while cases of chlamydia increase by 6.7 among 16-year-old women and 1.5 among 29-year-old women. Conclusions: Our findings indicate that the use of oral contraceptives among young people and young adults is positively associated with the chlamydia incidence and the abortion rate in these populations in Sweden.