Abstract
At the beginning of 1969 Swedish physicians were called upon by the National Board of Health and Welfare to report all pregnancies known to have occurred in women who had used oral contraceptives. Ninety pregnancies were reported for 1968, 73 of these with the sequential type of therapy and 17 with the combined type. Calculations using Pearľs formula and based on sales figures gave pregnancy rates of 0.467 and 0.005 for sequential and combined agents respectively. The possible causes of errors in these statistics are discussed. However, it is concluded that the pregnancy risk, is much more than ten times higher with the sequential than with the combined type of therapy. The most important cause of the failures in this series seems to have been the lack of efficacy of the drugs.