Potential Use of Immature Oocyte to Improve Fertility Preservation Outcome: A Narrative Review.

Fertility preservation through gamete vitrification has become one of the critical strategies to secure a childbearing potential in patients who are diagnosed with cancer or risks of infertility. Preserving the gametes would prevent the deleterious effects of cancer drugs or radiotherapy exposure on the quality of the gametes. Furthermore, fertilisation of vitrified mature human oocytes has lately demonstrated promising results that are reflected in the increased survival rate of thawed oocytes and the resultant clinical pregnancy rate. However, limitations in the cryopreservation of mature oocytes of cancer patients persist. Ovarian stimulation protocols which comprise administering gonadotrophin-releasing hormones could aggravate cancer or delay essential cancer therapy. Considering such circumstances, vitrification of immature oocytes would become a rational option. While the vitrification procedure of mature oocytes has been established, the vitrification of immature oocytes remains controversial due to a low post-thaw maturation and fertilisation rate. Apparent cryoinjuries to the immature oocytes post thawing or warming have been observed in both human and animal model oocytes. An alternative strategy was therefore proposed to improve the effectiveness of utilising immature oocytes for fertility preservation by conducting the oocyte maturation process first before vitrification. This method has prevailed, especially in oncofertility patients. Although the success rate of the clinical outcomes remains low, this approach, in conjugation with proper counselling, might provide oncofertility patients with an opportunity to preserve their reproductive potential.