A MATHEMATICAL-MODEL OF FOLLICLE DYNAMICS IN THE HUMAN OVARY

A mathematical model has been developed to describe the rates of growt h and death of follicles in human ovaries between 19 and 50 years of a ge, It was based on the numbers of follicles at three successive stage s of development, which were obtained by counting follicles in histolo gical sections of ovaries from 52 normal women, The model indicated th at follicle dynamics were age dependent, with a transition at 38 years of age when the rate of follicle disappearance increased, The rates o f follicle growth increased at successive stages but did not change wi th age, The annual egress from stage III (consisting of follicles with two or more granulosa cell layers) was affected by the declining numb ers of small follicles, and corresponded to 31, nine and one follicles per day at 29-30, 39-40 and 49-50 years of age respectively, The rate of death at stage I (representing small, resting follicles) was the o nly parameter which varied significantly with age: no evidence of sign ificant atresia was found for this stage in ovaries less than or equal to 38 years old, but there was significant death above this age, As a consequence, only 40% of follicles leaving stage I reached stage III in older ovaries and just 1500 follicles in tote remained at 50 years of age from the 300 000 present at 19 years, This high death rate of s mall follicles appears to be responsible for advancing the timing of o varian failure, and therefore of menopause, to midlife in our species.