Secular trend and intrapopulational variation in age at menopause in Spanish women

Menopause is associated with the general ageing process and marks the end o f follicular depletion, a process that begins in the intrauterine stage and lasts throughout the lifetime of women until their reproductive senescence . Controversy persists about whether the age at menopause is sensitive to t he ecological determinants prevailing during the lifecycle or whether it ha s a predominantly genetic component that would allow groups of women to be characterized with respect to particular menstrual characteristics manifest ed throughout their fertile life. By contrast, there is a definite secular trend in age at menarche in populations that have registered improvements i n their environment: sexual maturation is closely associated with the gener al processes of growth and development. These aspects were analysed in a sa mple of Spanish women, mothers and daughters, born between 1883 and 1941. T he results show (a) indications - although not conclusive - of a secular tr end in the age at menopause, (b) a possible association between the age at menopause of mothers and their daughters, and (c) an association at the ind ividual level between age at menarche, particular characteristics of ovaria n function (fetal loss) and age at menopause. The reproductive ageing proce ss therefore seems to result from the expression of the influence of ecolog ical conditions in which the lifecycle of the women develops and of a degre e of heritability that affects not only the age at menopause but also a ran ge of characteristics of ovarian function.