The fluid dynamics of ovulation were investigated to understand the mechani
cal role of follicular fluid in oocyte release. A set of equations describi
ng the flow of fluid from an evacuating follicle was derived from basic pri
nciples. These equations demonstrate that, subject to assumptions about the
available pressure differential and the source of the expulsive force, the
size and shape of the ovulatory orifice have the largest influences on the
rate of fluid loss, although the viscosity of the fluid is also an importa
nt variable. A thorough rheological examination of pig, bovine and human fo
llicular fluids, performed using a cone-plate viscometer, demonstrated that
these fluids have complex, non-Newtonian characteristics. The fluids also
undergo time-dependent and spontaneous changes in viscosity at constant she
ar rates; some fluids were subject to coagulation-like events. Viscosity ch
aracteristics were unrelated to broad parameters of follicle development. T
he models used representative viscosity values to demonstrate that variatio
ns in the rate and duration of follicle evacuation, as observed by ultrason
ography, could be explained largely by variations in fluid viscosity and th
e characteristics of the ovulatory orifice.