The design of a field trial depends principally upon precise definitions of terms to be used with universal application in all centres conducting the study. This goes also for recording events that occurred during the trial such as pregnancy and bleeding, local and systemic side effects. Advantage should be taken of these trials to conduct metabolic studies on patients undergoing long term therapy, and those patients who discontinue with a wish to become pregnant should be closely followed for the timing of restoration of fertility and the outcome of the subsequent pregnancy.
