The ovarian cycle refers to the monthly series of events in the ovaries, associated with the maturation and release of an ovum, and the 'just in case' preparation for its fertilisation and implantation in the uterus. You may be wondering why the regulation of the female reproductive system is so complicated, as shown in Figure 4.1. The reason is that the ovarian cycle has to be initiated (switched on) and then suppressed (switched off) in a precisely regulated sequence every month. In this section, we will explain how this is achieved.
The ovarian cycle consists of two consecutive phases, each of about 14 days' duration. Events are measured from 'day 1', which is the first day of the last normal menstrual period (LNMP).