Immature oocyte in-vitro maturation: clinical aspects

Impact of vitrification on human oocytes before and after in vitro maturation: A systematic review and meta-analysis

OBJECTIVE

There are controversies regarding in vitro maturation (IVM) procedure, the time of storing frozen oocytes and maturation stage of vitrified oocytes and its impact on oocytes fertilization capability. The aim of this systematic review and meta-analysis was to evaluate the impact of vitrification on human oocytes during IVM procedure.

STUDY DESIGN

A systematic review with meta-analysis was undertaken. Main search terms were those related key words. We searched Medline, Embase, Scopus and ISI web of science to detect English-language studies. The final search was performed on 27 January 2018. The original articles which studied laboratory outcomes after vitrification of MII or GV oocytes before or after IVM were included. Exclusion criteria were animal trials and the studies that performed cryopreservation using slow-freeze method. Oocyte maturation, survival, fertilization and cleavage rates were assessed. Bias and quality assessments were applied.

RESULTS

2476 articles were screened and after duplicates removing together with application of inclusion and exclusion criteria, 14 studies assessed for eligibility. Finally 5 studies included for analysis. All studies compared laboratory outcomes between oocytes that vitrified at the GV stage and those which firstly matured in vitro, and then vitrified. Meta-analysis showed that vitrification of oocytes at GV stage had a negative impact on maturation rate (RR = 1.28, 95% CI: 0.96-1.70); but not on cleavage rate (RR = 1.07, 95% CI: 0.70-1.64); fertilization rate (RR = 0.99, 95% CI: 0.85-1.14) and survival rate(RR = 1.01, 95% CI: 0.96-1.06).

CONCLUSION

In general, Based on our results, oocyte vitrification decreases the maturation rate. In addition, survival, fertilization as well as cleavage rates did not significantly differ between the oocytes vitrified before IVM versus oocytes vitrified after IVM.

In vitro maturation: Clinical applications

Oocyte in vitro maturation (IVM) is an assisted reproductive technology in which oocytes are retrieved from the antral follicles of unstimulated or minimally stimulated ovaries. IVM of human oocytes has emerged as a promising procedure. This new technology has advantages over controlled ovarian stimulation such as reduction of costs, simplicity, and elimination of ovarian hyperstimulation syndrome. By elimination or reduction of gonadotropin stimulation, IVM offers eligible infertile couples a safe and convenient form of treatment, and IVM outcomes are currently comparable in safety and efficacy to those of conventional in vitro fertilization. IVM has been applied mainly in patients with polycystic ovary syndrome or ultrasound-only polycystic ovaries, but with time, the indications for IVM have expanded to other uncommon situations such as fertility preservation, as well as to normal responders. In this review, the current clinical experiences with IVM will be described.

Granulocyte colony-stimulating factor (G-CSF): a mediator in endometrial receptivity for a patient with polycystic ovary (PCO) undergoing in vitro maturation (IVM)

Proliferative and secretory changes at the endometrial lining are the result of a complex intrauterine environment where sex steroid hormones and different local factors play an important role for endometrial thickening. Optimal endometrial thickness reflects an adequate maturation which is a key factor for embryo implantation. Here, we present a case of a woman with polycystic ovary who was treated using in vitro maturation (IVM) techniques. In addition, this patient showed a dyssynchrony between the endometrial phase characterised by endometrial thinning and the embryo development which had a negative impact for embryo implantation. A protocol using uterine perfusion of granulocyte colony-stimulating factor (G-CSF) was performed as an alternative treatment for the unresponsive endometrium. We found that uterine infusion of G-CSF quickly increased endometrial thickness resulting in a successful pregnancy and healthy born baby. These results suggest that G-CSF is a factor that participates during endometrial remodelling enhancing the synchronisation between uterine environment and embryo development.

In-vitro maturation of human oocytes: before or after vitrification?

PURPOSE

This study aims to determine if in-vitro maturation (IVM) of human immature oocytes should be performed before or after vitrification.

METHODS

A total of 184 immature oocytes were randomly divided into two different groups: 100 were vitrified at metaphase II (MII) stage 24 h-48 h after IVM (group 1) and 84 were immediately vitrified at germinal vesicle (GV) or metaphase I (MI) stages and in vitro matured after warming (group 2).

RESULTS

Survival rate after warming was similar in both groups (86.9% versus 84.5%). However, oocyte maturation rate per collected oocyte was significantly higher for oocytes matured before vitrification (group 1, 46%) than for oocytes vitrified before IVM (group 2, 23.8%) (p < 0.01). Consequently, the number of MII oocytes inseminated per oocyte collected was significantly higher for group 1 (40%) than for group 2 (23.8%) (p < 0.05).

CONCLUSION

IVM procedure is more efficient when it is performed before oocyte vitrification.

Controversies in IVM

PURPOSE

To explore four areas of controversy: the benefits of gonadotropin priming, benefits and timing of hCG trigger as well as the ideal protocols for endometrial preparation and luteal support.

METHODS

A literature review was performed to explore the current evidence

RESULTS

Current evidence suggests that Gonadotropin priming in combination with hCG prior to collection benefits patients with normal ovaries. In PCOS patients 10,000 IU hCG 38 h before retrieval increases the total number and rate of oocyte maturation. Gonadotropin priming may also benefit PCOS patients. The ideal timing of hCG trigger appears to be when the leading follicle is 10-12 mm. Sparse data exists regarding luteal support protocols.

CONCLUSIONS

There is still a need for well-designed studies to establish ideal methods for oocyte priming, timing of retrieval, endometrial preparation and luteal support. Further studies must incorporate both clinical and basic science principles of ovarian, follicular and endometrial physiology.

Contribution of in-vitro maturation in ovarian stimulation cycles of poor-responder patients

This cohort study evaluated whether rescue spontaneous maturation (RSM) could be a valid method to increase the number of embryos available for transfer and whether transfers with RSM-derived embryos would contribute to clinical outcomes of poor-responder patients in ovarian stimulation cycles. The study included 440 patients undergoing intracytoplasmic sperm injection cycles in which fewer than five metaphase II (MII) oocytes and at least one immature oocyte were retrieved after follicle aspiration. Patients were allocated into two groups based on the injected oocytes' nuclear maturation status: MII group (n=330), in which only embryos derived from MII oocytes were transferred, and RSM group (n=110), in which at least one embryo derived from an RSM oocyte was transferred. No differences between the MII and RSM groups were observed for pregnancy (16.7% versus 16.5%) or miscarriage (25.5% versus 29.4%) rates, respectively. The RSM group had a higher number of transferred embryos (1.87+/-1.24 versus 2.35+/-1.22; P<0.001), a lower embryo transfer cancellation rate (14.5% versus 6.36%; P=0.025) and lower implantation rate (15.4+/-31.5% versus 10.5+/-22.3%; not significant). These findings suggest that RSM did not contribute to the outcomes in poor-responder cycles.

Could oxidative stress influence the in-vitro maturation of oocytes?

In the efforts aimed at improving the quality of in-vitro-matured human oocytes, the dynamic balance and roles of pro-/antioxidants merit further consideration. In-vitro maturation (IVM) is emerging as a popular technology at the forefront of fertility treatment and preservation. However, standard in-vitro culture conditions exert oxidative stress or an imbalance between oxidants and antioxidants. Reactive oxygen species (ROS) are oxygen-derived molecules formed as intermediary products of cellular metabolism. By acting as powerful oxidants, ROS can oxidatively modify any molecule, resulting in structural and functional alterations. ROS are neutralized by an elaborate defence system consisting of enzymatic and nonenzymatic antioxidants. This review captures the inherent and external factors that may modulate the oxidative stress status of oocytes. It discusses the suspected impacts of oxidative stress on the gamut of events associated with IVM, including prematuration arrest, meiotic progression, chromosomal segregation, cytoskeletal architecture and gene expression. In-vivo and in-vitro strategies that may overcome the potential influences of oxidative stress on oocyte IVM are presented. Future studies profiling the oxidative stress status of the oocyte may permit not only the formulation of a superior IVM medium that maintains an adequate pro-/antioxidant balance, but also the identification of predictors of oocyte quality.

Developmental competence of immature and failed/abnormally fertilized human oocytes in nuclear transfer

Somatic cell nuclear transfer holds great promise for basic studies of reprogramming human somatic cells and for the potential development of novel cell-based therapeutics. The aim of this study was to examine experimental aspects of human nuclear transfer via use of an abundant source of oocytes, those that are routinely discarded from assisted reproduction clinics. The results suggest and reinforce several findings based on the analysis of multiple parameters: first, it was observed that supplementation of commercial culture media with hormones promoted embryo development after parthenogenetic activation. Second, the use of the chemical activation reagent puromycin resulted in significant differences in cleavage rates in oocytes that were failed/abnormally fertilized after intracytoplasmic sperm injection relative to those from IVF (P < 0.05). Third, cycloheximide promoted cleavage rates >/=40% in both groups of oocytes; moreover, two blastocysts were produced following cycloheximide treatment. Finally, the use of a subset of oocytes for nuclear transfer resulted in cleaved embryos that expressed green fluorescent protein from a transgene in donor nuclei from human embryonic stem cells. In light of these results, it is suggested that the discarded oocytes can be used to investigate new human nuclear transfer protocols for embryonic stem cell derivation.

Combining ovarian tissue cryobanking with retrieval of immature oocytes followed by in vitro maturation and vitrification: an additional strategy of fertility preservation

OBJECTIVE

To report an additional strategy of fertility preservation, which combines ovarian tissue cryobanking with retrieval of immature oocytes from excised ovarian tissue, followed by in vitro maturation (IVM) and vitrification.

DESIGN

Retrospective analysis of case series.

SETTING

University teaching hospital.

PATIENT(S)

Women who underwent oophorectomy or ovarian wedge resection before receiving chemotherapy and/or radiotherapy.

INTERVENTION(S)

Immature oocyte retrieval, IVM, oocyte vitrification, ovarian tissue cryobanking.

MAIN OUTCOME MEASURE(S)

Oocytes retrieved from the excised ovarian tissue, oocyte maturation rate, and number of oocytes cryopreserved by vitrification.

RESULT(S)

Four consecutive patients underwent retrieval of immature oocytes from the antral follicles of the excised ovarian tissue. The mean number of immature oocytes recovered was three (1, 3, 4, and 3, respectively). The mean maturation rate following IVM was 79% (100%, 100%, 50%, and 67%, respectively). In total, eight mature oocytes were vitrified.

CONCLUSION(S)

Oocytes can be retrieved from excised ovarian tissue, matured in vitro, and cryopreserved by vitrification. This fertility preservation technique could be combined with ovarian tissue cryobanking.

Prognostic value of meiotic spindle imaging on fertilization rate and embryo development in in vitro-matured human oocytes

OBJECTIVE

To evaluate the relationship between spindle visualization and intracytoplasmic sperm injection (ICSI) outcomes in controlled ovarian stimulation (COS) cycles.

DESIGN

Prospective study.

SETTING

Assisted reproduction center.

PATIENT(S)

Thirty patients undergoing ICSI cycles.

INTERVENTION(S)

Meiotic spindle was evaluated before ICSI in 234 in vivo- and 101 in vitro-matured oocytes

MAIN OUTCOME MEASURE(S)

Meiotic spindle imaging, fertilization rate, and embryo development.

RESULT(S)

Spindle was present in 74.3% and 73.8% of the in vivo- and in vitro-matured oocytes, respectively. Spindle detection rate in oocytes derived from germinal vesicle and metaphase-I stage was, respectively, 50% and 86%. The fertilization rate achieved by the in vivo-matured oocytes was 71.8%, and spindle was detected in 75.6% of the fertilized oocytes and only 34.8.% of the nonfertilized oocytes. In the in vitro-matured oocytes, the fertilization rate was 66.1%, and spindle was detected in 81.4% of the fertilized oocytes and in 59.1% of the nonfertilized oocytes. Ten out of 43 (23.2%) in vitro-matured derived embryos were considered to be high quality, all derived from spindle-detected oocytes, which represents an increase of 13.0% on the overall number of high-quality embryos.

CONCLUSION(S)

Meiotic spindle imaging may be useful to predict in vitro-matured oocyte development. However, other factors may contribute to the decreased developmental competence of in vitro-matured oocytes.

In-vitro maturation of oocytes: biological aspects

Natural cycle and in-vitro maturation (IVM) of oocytes are becoming interesting alternatives to classical assisted reproduction technology approaches for patients, especially in those at high risk for ovarian hyperstimulation syndrome or with poor ovarian reserve. More than for their clinical and biological indications, natural cycle and IVM of oocytes can also be considered as good social and economic alternatives to the classical IVF treatment, based on their financial cost-effectiveness with exclusion of expensive medications. To be successful, IVM must entail both nuclear and cytoplasmic maturation, and its maturation and success rates are affected by the number of collected cumulus layers, the degree of atresia and the maturation rate between 24 and 48 h. Endogenous regulation of oocyte maturation is a complex sequence of events regulated by endocrine parameters, oocyte/follicular cross-talk, and intra-oocyte kinase/phosphatase interactions. This complex process requires a better definition of each contributing factor affecting oocyte development and the resulting embryo quality. The clinical aspects of IVM have been documented earlier; the present paper will mainly focus on the biological aspect of oocyte maturation in vitro and the quality of derived embryos.

Effect of gonadotrophin stimulation on mouse oocyte quality and subsequent embryonic development in vitro

In-vivo-matured oocytes were collected from naturally ovulated and superovulated [pregnant mare's serum gonadotrophin (PMSG) + human chorionic gonadotrophin (HCG)] mice. Immature oocytes were retrieved from naturally cycling mice and from mice primed with PMSG. The percentages of cleavage and blastocyst formation were significantly different (P < 0.05) between in-vivo- and in-vitro-matured oocytes. Blastocyst formation rate was significantly higher (P < 0.05) in immature oocytes derived from PMSG-primed mice, and the percentages of oocytes with comet tails, and their length, were significantly higher and longer respectively in in-vitro-matured oocytes. Total cell numbers of blastocysts were also significantly different (P < 0.05) between in-vivo- and in-vitro-matured oocytes, but there were also no differences in ratio of trophectoderm (TE)/inner cell mass (ICM). In conclusion, in-vivo-matured mouse oocytes were more competent than those matured in-vitro, perhaps due to a lesser degree of DNA damage. Embryonic development capacity of in-vivo-matured oocytes is not promoted by ovarian stimulation. Gonadotrophin priming prior to immature mouse oocyte retrieval is beneficial to subsequent embryonic development.

Comparative maturation of cynomolgus monkey oocytes in vivo and in vitro

BACKGROUND

In vitro maturation (IVM) of oocytes followed by fertilization in vitro (IVF) and embryo transfer offers an alternative to conventional IVF treatment that minimises drug administration and avoids ovarian hyperstimulation. However, the technique is less efficient than maturation in vivo. In the present study, a non-human primate model was used to address the hypothesis that the number of oocytes is increased and their nuclear and cytoplasmic maturity after IVM are improved when maturation is initiated in vivo by priming with hCG.

METHODS

Young, adult cynomolgus monkeys were given recombinant human (rh) gonadotropins to stimulate the development of multiple follicles, and oocytes were aspirated 0, 12, 24, or 36 h after injection of an ovulatory dose of rhCG. The nuclear status of oocytes was determined at the time of recovery and after culture for a total elapsed time of 40-44 hours after hCG.

RESULTS

Priming with hCG significantly increased the number of oocytes harvested, especially after delaying aspiration for 24 h or longer. Nuclear maturation after the full period in culture was also enhanced by priming: 71.5, 83.6, and 94.6% of oocytes collected at 0, 12, and 24 h hCG had progressed to MII by the end of the culture period, compared to 87.8% of oocytes that were retrieved at 36 h. A large proportion of oocytes reaching the MII stage had either or both abnormal spindles (>40%) and misaligned chromosomes (>60%), judging by immunofluorescence microscopy, but these abnormalities were independent of culture time. The mitochondria were evenly distributed throughout the cytoplasm at all stages of maturation. Importantly, there was no microscopic evidence that the duration of culture had any injurious effects on the cells.

CONCLUSION

In conclusion, the evidence supports this non-human primate as a model for human IVM and the practice of priming with hCG to promote developmental potential.

Timed IVM followed by ICSI in a patient with immature ovarian oocytes

A complete failure of meiotic maturation occasionally occurs following human chorionic gonadotrophin administration during IVF-intracytoplasmic sperm injection (ICSI) cycles. ICSI on day 1 is commonly used to allow maturation in culture. However, if the oocytes become mature in the evening soon after their recovery but ICSI is delayed until the next day, then subsequent ageing of matured oocytes may be unfavourable for fertilization and development. To avoid the deterioration associated with oocyte ageing, the timing of polar body extrusion was checked every 3 h and rescue in-vitro maturation (IVM)-ICSI was performed shortly after the polar body extrusion was confirmed. This report describes a successful pregnancy and birth of a healthy baby in a patient who had no mature oocytes at the time of oocyte retrieval, and illustrates the value of extra monitoring for IVM and ICSI in cases where only immature oocytes are available.

IVM – the first choice for IVF in Italy

In March 2004, a new law was introduced in Italy to regulate assisted reproduction; at present it is impossible to use more than a maximum of three oocytes per IVF cycle, nor can embryos or prezygotes (2PN cells) be selected or cryopreserved. The prohibitions introduced by the new law have, on the one hand, reduced the expectations of success of current techniques and, on the other hand, stimulated clinicians and embryologists to work on new therapeutic strategies so as to offer the highest chances of success with the lowest risks. In-vitro maturation (IVM) of oocytes fits very well with these new requirements: ovarian stimulation is avoided and the handling of spare oocytes is facilitated. The IVM protocol is an intriguing alternative to conventional IVF techniques, since it removes the side-effects of drug stimulation, especially ovarian hyperstimulation syndrome, and it also reduces the costs of the entire procedure, both in terms of 'time consumption' and 'patient/society costs for drugs'. In the authors' IVF centre the IVM technique has been used for more than a year, with significant success in terms of maturation and fertilization rates, percentage of embryo transfers, number of pregnancies and, finally, healthy babies born.

Successful birth after injection of frozen human oocytes with frozen epididymal spermatozoa

A couple (female 31, male 42 years old) with infertility due to obstructive azoospermy returned to the clinic in order to attempt pregnancy using their frozen oocytes and epididymal sperm cells, which had been cryopreserved at the time of a previous IVF attempt. Two days before the scheduled transfer, eight oocytes were thawed; 5/8 (63%) oocytes survived and 4/5 (80%) oocytes fertilized after intracytoplasmic sperm injection (ICSI) with the previously frozen epididymal spermatozoa. All four fertilized ova cleaved (100%). On day 2 after thawing, four embryos were transferred; three with two cells (grade II) and one with three cells (grade III). Hormonal support for the established pregnancy was maintained with oestradiol and progesterone orally until 12 weeks of gestation, and the patient was delivered by Caesarean section at 40 weeks of gestation; the baby boy weighed 3025 g, and measured 51 cm, with Apgar of 10 in the 1st and 5th min. The cryopreservation and warming protocol used for this study yielded very favourable results, comparing well with reports in the literature. This case report demonstrates that it is possible to obtain high rates of oocyte survival following thawing and high rates of fertilization after ICSI, with viable development of the resulting embryos.