The role of in vitro maturation in fertility preservation

Abstract

In vitro maturation (IVM) is an advanced embryology laboratory technique in which immature oocytes, removed from ovarian follicles prior to completing their growth in vivo, are cultured to meiotic maturation in vitro. Mature eggs are then either cryopreserved or they are fertilized and the resulting embryos cryopreserved for later use. While IVM techniques are considered experimental, they can be completed rapidly (within 1–2 days) with no need for hormonal stimulation, making IVM a potentially useful fertility preservation intervention for women who cannot postpone cancer treatment or who have estrogen-sensitive cancers. Meticulous lab technique and advanced surgical skills are necessary for a successful IVM program, and a historical review of the procedure and advances in surgical techniques and protocols are described. Oocyte harvesting methods, either through in situ intravaginal aspiration or in vitro from ovarian tissue samples, are discussed, as are techniques for identifying immature oocytes, determining nuclear meiotic status, culturing, and monitoring for meiotic maturation. Intracytoplasmic sperm injection (ICSI) is the most common procedure for fertilizing in vitro-matured eggs for cryopreservation of embryos, and cryopreservation of oocytes can occur either before or after completion of meiosis. This chapter concludes with a discussion of IVM pregnancy outcomes as well as future directions for IVM of immature oocytes retrieved from banked ovarian tissue (in vitro follicle maturation).