Abstract

PIP: The Oxford Family Planning Association (Oxford, England) contraceptive study has yielded data on the efficacy of a wide range of birth control methods for a large, homogeneous group of married women attending family planning clinics. Some of the main findings are summarized in the hope that they may be of direct value to the practicing physician. 17,032 women were recruited from 17 large family planning clinics in England and Scotland during 1968-1974. At recruitment, every woman was aged 25-39 years, married, a white British subject, willing to participate, and either a current user of oral contraceptives (OCs) of at least 5 months' standing or a current user of a diaphragm or an IUD of at least 5 months' standing without prior exposure to the pill. On return visits to the clinic, each woman is questioned and data, including details of all pregnancies and any change in contraceptive practice together with reasons for the change, are recorded on a special form. In the analyses which follow, the failure rates represent "use-effectiveness," i.e., they include accidental pregnancies attributable both to failure of the method and to failure by the woman to use the method correctly. Overall failure rates for the different contraceptive methods together with 95% confidence limits are shown in a table. The failure rate/100 woman-years is as follows: for combined OCs with more than 50 mcg estrogen--0.32, with 50 mcg estrogen--0.16, and with less than 50 mcg estrogen--0.27; progestogen-only OC, 1.2; diaphragm, 1.9; condom, 3.6; Lippes loop A 6.8; Lippes loop B, 1.8; Lippes loop C, 1.4; Lippes loop D, 1.3; Saf-T-Coil, 1.3; Dalkon shield, 2.4; Birnberg bow, 1.6; Antigon, 0.4; M-213, 1.3; Copper-T, 1.2; Copper-7, 1.5; Multiload, 0.0; type unknown, 1.8; rhythm, 15.5; coitus interruptus, 6.7; chemicals alone, 11.9; female sterilization, 0.13; and male sterilization, 0.02. Sustained motivation is essential for effective use of contraceptive methods requiring deliberate action on the part of the user. Accordingly, the failure rates were analyzed for OC users, diaphragm and condom users in relation to the only direct indicator of motivation recorded in the study, i.e., whether or not a woman considered her family to be complete. A substantial effect was apparent only for diaphragm users.