The life expectancy of women has increased significantly over the past century and the advent of efficient contraception has given women the opportunity to choose when to have children. At present many women delay childbearing for a variety of social and economic reasons, including higher education, a career and economic pressure to remain at work, that have contributed to a constant increase in older women seeking treatment for infertility (Medical Research International, 1990). The trend towards older parenting is evident in the general population (Baldwin & Windquist Nord, 1995) and the number of births for every thousand British women in their early 30s has exceeded that of women in their early 20s (Office of Population Censuses and Surveys, 1994).

Fecundity

Female fecundity is generally acknowledged to decrease by the age of 30 years (van Noord-Zaadstra et al., 1991; Leridon, 1977). The decline is gradual until a rapid decline from the age of 35 years and by the age of 45 years fecundity is almost lost (Navot et al., 1987).Women aged over 35 years take longer to conceive and a higher proportion will never achieve a pregnancy when compared to younger women (Navot et al., 1991). This decline is related to a process of follicular depletion and diminished oocyte quality.

Follicular depletion

The ovarian function is limited by the size of the follicular store laid down prenatally. Approximately seven million human germ cells are formed in fetal ovaries, with only two million remaining at birth and around 300 000 remaining at the menarche (Gosden, 1987). The reduction in the number of oocytes is a dynamic process that continues throughout a woman's premenarcheal and menstrual life.