The relative reliability of oral contraceptives; findings of an epidemiological study

A study performed in The Netherlands shows that an undesired pregnancy, claimed to be due to "method failure" with oral contraceptive use and resulting in a request for induced abortion, occurs approximately twice per 10,000 woman-years. For these claimed method failures the type of pill used has been recorded during the years 1982-1984. From those data it is clear that the usage of sequential and triphasic OCs was found to be significantly more often amongst women who requested abortion than would have been expected on the basis of their usage in the general population. This over-representation of sequential and triphasic OCs could not be explained by gastro-intestinal disorders or by drug-interaction.