Ovarian stem cells are oocytes formed in ovarian follicle before birth in female mammals. Interest has recently been devoted to OSCs (ovarian stem cells), whose isolation from female ovaries, followed by their in vitro culture, led to their maturation to OLCs (oocyte-like cells), namely, neo-oocytes comparable to viable eggs suitable for IVF. Translation of these data to FP clinical application creates new hope in the treatment of infertility.

Studies performed on humans, dogs, and cats revealed that oocyte production stops shortly after birth. If this is true, it would mean that females have a finite number of oocytes that are formed before they are born.

Studies demonstrated that 'new' oocytes could be produced after damage to the fowl ovary. Additional research demonstrated that rats which had one ovary removed before puberty produced the same number of mature eggs as healthy rats. This would suggest that some compensatory mechanism is at work; an increase in immature follicle development could have occurred, or post-natal oogenesis may have been activated. However, such theories were merely speculative.

Sir Solomon Zuckerman examined reports from 1900 to 1950 of multiple species and concluded that "no experimental or histological evidence supports the view that oogenesis continues after puberty". This dogma was rarely challenged.

Studies in adult primates demonstrated the presence of oogonia in mitosis as well as oocytes at successive stages of meiosis, leading to the conclusion that postnatal oogenesis takes place. Mitotic cells were not specifically stained for oocyte markers, so identification was limited to histological analysis of haematoxylin-stained sections. It is therefore possible that granulosa/theca cells, or other support cells within the ovary, could be dividing.

Drosophila melanogaster's postnatal oogenesis cycle is well characterized; however, invertebrates lack the genetic similarity to allow translation of the same findings into mammals.

Mice were found to have presumptive oocyte stem cells (OSCs) expressing mitotic gene markers, indicating that they were dividing. A potential functional role of OSCs in vivo has also been demonstrated by the growth of GFP-labeled OSCs into follicles when transplanted into wild-type mouse ovaries. There is widespread scientific disagreement about whether mammalian oogenesis occurs post-natally.

In female human cancer patients that were treated with ABVD (adriamycin, bleomycin, vinblastine and dacarbazine) led to an increase in mean follicular density. So perhaps under certain perturbed circumstances, OSCs (if they exist) can be stimulated to form follicles.