Use-effectiveness of the diaphragm in a selected family planning clinic population in the United Kingdom

4052 established users of the diaphragm aged 25–39 years attending family planning clinics in the United Kingdom have been followed during 5909 woman-years of exposure to the risk of pregnancy. 139 accidental pregnancies have been observed, representing a use-effectiveness pregnancy rate of 2.4 per 100 woman-years. Of the factors related to the risk of accidental pregnancy, the age of the user and the duration of use of the diaphragm appear to be the most important.It is concluded that women attending family planning clinics who are already established users of the diaphragm need not be encouraged to change to a more modern method of birth control with its attendant risks.