Human oocyte maturation in vitro

Abstract

Oocytes from medium-sized antral follicles have already completed their growth phase and, if released from the follicular environment and cultured in vitro, are able to resume the meiotic process and mature. However, in vitro maturation (IVM) does not entirely support all the nuclear and cytoplasmic changes that occur physiologically as an effect of the ovulatory stimulus. Regardless, oocyte IVM is widely applied for the breeding of agriculturally important species. In assisted reproduction technology, IVM has been proposed as an alternative treatment to circumvent the drawbacks of standard ovarian stimulation regimens. Initially introduced to eliminate the risks of ovarian hyperstimulation syndrome afflicting women presenting with polycystic ovaries, subsequently IVM has been suggested to represent an additional approach suitable also for normovulatory patients. So far, in children born from IVM cycles, no doubts of an increased incidence of congenital abnormalities have been raised. Many more births would be achieved if novel IVM systems, currently dominated by empiricism, could be conceived according to more physiological criteria. Recent findings shedding new light on the control of meiotic progression, the support of cumulus cells to the oocyte cellular reorganization occurring during maturation, and the modulation of the stimulus that promotes oocyte maturation downstream the mid-cycle gonadotropin signal are likely to provide crucial hints for the development of more efficient IVM systems.

Assessment of the Field of Assisted Reproductive Technology: Improvements and the Future of Human In Vitro Fertilization

“…However, in treatment cycles where hormone levels were not thought to be a risk or concern, such as in normo-ovulatory patients, human chorionic gonadotropin (hCG) and follicle-stimulating hormone (FSH) are used to "prime" ovaries, typically called hCG and FSH priming, respectively [9,76,77]. IVM eliminates the need for excess gonadotropin stimulation to induce ovulation because the oocytes are collected while still of smaller size and are grown in vitro instead of in vivo [78]. The goal of IVM is to reduce or completely eliminate disadvantages associated with the typical IVF procedure, including the cost of hormonal administration, risk of ovarian hyperstimulation syndrome (OHSS), and the inestimable burden on patients [79].…”

“…Additionally, major concerns were allayed when data indicated that there was no increased incidence of congenital abnormalities or perinatal complications with usage of IVM [78]. Despite this, IVM is not widespread for a few reasons: PCOS women only represent 5-10% of ART patients, normo-ovulatory women do not typically have enough antral follicles required for early oocyte retrieval in IVM, and lastly, due to in vitro matured oocytes having a reduced developmental potential compared to those matured in vivo [10,78,81].…”

“…There is substantial room for improvement and study in IVM procedures, including but not limited to the administration of estrogen and progesterone, the additives in the culture, and the gonadotropins utilized [78]. Ample evidence has shown that hCG priming enhances oocyte maturation and clinical pregnancy rates, while evidence for FSH priming remains limited; however, because FSH is believed to improve follicular health and to increase the quantity and quality of oocytes, especially in PCOS patients, some studies continue to include this step while others have removed FSH priming from their protocols [78,80,[82][83][84][85].…”

“…Ample evidence has shown that hCG priming enhances oocyte maturation and clinical pregnancy rates, while evidence for FSH priming remains limited; however, because FSH is believed to improve follicular health and to increase the quantity and quality of oocytes, especially in PCOS patients, some studies continue to include this step while others have removed FSH priming from their protocols [78,80,[82][83][84][85]. By investigating these topics, the obstacles of lower implantation and maturation rates may be overcome.…”

“…At the present, there is limited data on using IVM with IVF in normo-ovulatory women as well as the implantation and pregnancy rates as compared with conventional IVF [88]. The relatively few studies published indicate not only decreased embryo quality and viability but also a significantly lower implantation rate following IVM with IVF versus that of conventional IVF [8,77,78,83]. While advances have been made as to improving IVM protocol and ensuring better success with embryo transfer, due to the nature of patients undergoing IVM significantly larger numbers of embryos are needed for transfer to ensure comparable rates to IVF [9,89].…”