Fully mature oocytes are the rarest cells in the body. A premenopausal woman produces only one during each menstrual cycle and that survives for just a single day. Ovarian productivity is parsimonious in order that the ovulation rate matches the optimal capacity of the uterus for carrying conceptuses to full-term. But, in this new era of assisted reproductive medicine, there are many applications for which spare oocytes are needed (Table 1), and it is desirable to obtain more cells than are routinely available during superstimulated cycles. Since the great majority of ovarian oocytes undergo atresia (> 99.9%), the possibility of tapping the store of immature oocytes before they degenerate and maturing them in vitro is very attractive.

Several conclusions can be drawn from a review of the formation, function and regression of the corpus luteum. Ovulation and luteinization encompass degenerative and growth changes. Inflammatory conditions associated with ovulation lead to the breakdown of the follicle wall and the membrana granulosa, along with initial damage to theca and granulosa cells. The early corpus luteum is, therefore, a tissue in stress. Thus, one view of the corpus luteum is that it, like the phoenix, rises from the inflammatory ashes of the postovulatory follicle to exist briefly and to be consumed by a similar process at regression. The luteinization process is associated with parenchymal cell hypertrophy and matrix remodelling, which appear to be regulated by IGFs and androgens, and with angiogenesis, which is induced mostly by bFGF. High levels of functional activity of the corpus luteum are regulated by control at the level of the LH receptor, whose activation leads to the translocation of cholesterol into the cell and mitochondria for conversion to steroids. Functional luteal regression can be considered as another inflammatory-like condition with apparent activation of the immune system, along with cytokine, reactive oxygen, and eicosanoid production. Structural luteolysis is subsequently invoked that leads to matrix dissolution and cellular degeneration. It is perhaps not surprising that the invocation of immune activation, which causes the production of DNA-damaging reactive oxygen species and cytotoxic cytokines each cycle, may increase the risk of pathologies. One example may be ovarian cancer which appears to be associated with the use of fertility-enhancing drugs and associated with the number of ovulations in a woman's lifetime.

Uterine fibroids are estimated to affect up to 25% of women of reproductive age and are a common cause of morbidity, being associated with menstrual dysfunction, iron deficiency anaemia, pregnancy wastage and subfertility. Their pathogenesis remains unknown but their association with ovarian function and oestrogen production is undisputed and supported by their occurrence only after puberty and the shrinkage observed after the menopause. This oestrogen dependency has recently been exploited therapeutically through investigation of the use of agents that induce a hypo-oestrogenic state, the gonadotrophin-releasing hormone (GnRH) or luteinizing hormone-releasing hormone (LHRH) analogues.

Micromanipulation technology entered the forum of human conception in vitro in the late 1980s. It was erroneously perceived as a new technology – a purely mechanical approach to bypass failures of conception in vitro, the aetiology of which were unknown. In fact, it is the modification of technology developed since the beginning of this century, and its logical utilization for conception in vitro, preconception (polar body) biopsy and preimplantation (blastomere and trophectoderm) biopsy in the realm of human infertility and genetic disorders.