Figure 3.

Main designs for time to pregnancy studies (27). The start date may be either the discontinuation of a method to avoid pregnancy or the end of a pregnancy not followed by use of methods to avoid pregnancy. The stop date may be the beginning of a pregnancy (detected later), the resumption of any method to avoid pregnancy (contraception, sexual abstinence), or the initiation of medical treatment for infertility. These last 2 situations correspond to censoring events. Duration 5 (pregnancy-based design) is assessed only if a pregnancy is detected at the end of the period of unprotected intercourse.