FSH and the control of follicular growth

During 70 days or so from the time of recruitment until just before the beginning of the cycle during which a follicle is destined to ovulate, folliculogenesis is a continuous process dependent on gonadotrophins but independent of the fluctuations in their concentrations occurring during this time. For follicle growth to continue beyond the 2-4 cell antral stage FSH concentrations must rise above a certain threshold level at the correct time. Once threshold levels are exceeded a single follicle becomes dominant suppressing FSH concentrations to subthreshold values. The period during which FSH concentrations are above threshold can be imagined as a gate through which a follicle must pass if it is to ovulate.