8 - The science of ovarian ageing: how might knowledge be translated into practice?

Summary

Introduction

Fecundity declines as women age, owing to the continual loss of oocyte-containing follicles from their ovaries and the simultaneous reduction in oocyte and embryo quality. At around 38 years of age, several years before the menstrual cycle ceases, the rate of oocyte loss increases towards total depletion of the follicular stock. The associated increase in circulating follicle-stimulating hormone (FSH) reflects the accelerated follicular loss and explains several features of ovarian ageing, including shortening of the follicular phase of the menstrual cycle and increased incidence of dizygotic twinning. The concomitant decrease in oocyte quality is in line with the increased incidence of miscarriages and chromosomal aberrations that occur after the age of 35 years. This chapter briefly reviews key aspects of the autocrine, paracrine and endocrine control systems involved and flags the most helpful diagnostic biomarkers of ovarian ageing. The conclusion is that little or nothing can be done at the moment to slow the process. However, if the mechanisms involved can be better understood, ovarian stimulation to obtain oocytes for assisted reproductive technology procedures from older women could be conducted more efficiently and effectively on a case-by-case basis.

Why ovaries shrink with age

Newborn girls' ovaries contain a finite stock of around seven million oocytes as non-growing primordial follicles. Each primordial follicle comprises an oocyte in the prophase of the first meiotic division, surrounded by an incomplete or whole layer of flattened spindle-shaped cells and separated from the surrounding ovarian stroma by a basement membrane.