Figure 1.
Timeline of a hypothetical woman's reproductive lifespan between menarche and menopause, with key events indicated by triangles (solid for visible events, shaded for transitions or hidden events). Fertility is shown as N births (B1 through BN) that occur during a primary window of fecundity (unshaded). Although not shown here, some births could occur during periods of subfecundity (shaded). (For simplicity, periods of temporary infecundity and subfecundity following births are not shown.) Reproductive stopping occurs with the last birth, BN, at ALB (age at last birth). Following BN, the time durations between events are denoted as shown by a, b, c and d, where d is the time from menopause to death. The time from last birth to menopause is thus a + b + c, and the post-reproductive lifespan is a + b + c + d. In theory, only the time between BN and death constrains the values of a, b, c and d, although c ≥ 1 year by definition of menopause.