High survival rate of metaphase II human oocytes after first polar body biopsy and vitrification: determining the effect of previtrification conditions

Cryopreservation of eggs

Oocyte cryopreservation is playing an increasingly important role in the field of human infertility treatment. The ability to store viable oocytes for later use has given many women the option to delay childbearing in order to pursue other ventures in life, without the concern of losing the opportunity to have a family. Furthermore, oocyte cryopreservation is very valuable for diseased patients who have to undergo treatments that may compromise fertility. Also, infertility patients who produce large numbers of oocytes during a retrieval cycle now have the option of storing some eggs prior to fertilization, thereby reducing the number of embryos that have to be managed. Lastly, oocyte cryopreservation enables egg donation programs that are independent of fresh donations, which makes it possible for numerous recipients to benefit from a single donor.Traditionally, slow freezing was the only method available for oocyte cryopreservation. However, recent years have shown that ultrarapid cooling of oocytes results in higher survival and developmental rates. Thus, vitrification is today's preferred method of oocyte cryopreservation and therefore the only technique described.In this chapter, we present two reliable methods of oocyte vitrification that have been in use for several years and that have been experimentally validated. Since no single vitrification method is clearly superior to the rest, other systems are also briefly described to give the reader options when deciding which methods to utilize in their practice.

Is vitrification of oocytes useful for fertility preservation for age-related fertility decline and in cancer patients?

The aim of this review is to provide current knowledge on oocyte cryopreservation, with special emphasis on vitrification as a means to preserve fertility in different indications. Major advancements achieved in the past few years in the cryolaboratory have facilitated major changes in our practice. Areas such as fertility preservation for social or oncologic reasons, the possibility to create oocyte banks for egg donation programs, the opportunity to avoid ovarian hyperstimulation syndrome, or to accumulate oocytes in low-yield patients, or even to offer treatment segmentation by stimulating the ovaries, vitrifying, and then transferring in a natural cycle are some of the options that are now available with the development of cryopreservation. We present general experience from our group and others on fertility preservation for age-related fertility decline as well as in oncologic patients, confirming that oocyte vitrification is a standardized, simple, reproducible, and efficient option.

Optimized protocol for cryopreservation of human eggs improves developmental competence and implantation of resulting embryos

Background

Successful egg cryopreservation has many potential benefits to a variety of patients. However, a superior standard protocol describing all aspects of oocyte cryopreservation has not yet been identified. Oocyte cryopreservation is still a technical challenge for many infertility clinics. To maintain satisfactory clinical outcomes, there is a need to develop an easy to use, yet efficient laboratory protocol. The present study was designed to examine if human embryos resulting from eggs frozen with an optimized vitrification protocol have similar developmental competence as those from fresh eggs.

Methods

Twenty recipients received donated eggs vitrified with a protocol in which short exposure time to the vitrification solution was used and 23 recipients received donated eggs and 6 patients had their own eggs vitrified with a modified protocol in which long exposure time to the vitrification solution was used. After warming, egg survival, fertilization, cleavage, blastocyst formation, clinical pregnancy and implantation rates were compared. The developmental competence of eggs vitrified with the optimized protocol was further compared with fresh eggs donated from the same donors.

Results

There was no difference in the oocyte survival, fertilization, cleavage, clinical pregnancy or implantation rates between the short and long protocol groups. However, blastocyst formation rate was significantly (P < 0.001) higher in the long protocol group (50.8%) than that in short protocol group (26.5%), resulting in more blastocysts being transferred and frozen. When frozen eggs vitrified with long protocol and fresh eggs from the same donors (12) were compared in 39 recipients, no differences were observed in terms of fertilization (86.4 vs 80.1%), blastocyst formation (50.0 vs 59.2%), clinical pregnancy (63.2 vs 60.0%) and implantation (41.7 vs 44.7%) rates. Four out of 6 patients had ongoing pregnancy after transfer of embryos from their own frozen eggs with a 46.2% implantation rate.

Conclusions

These results indicate that blastocyst development is an appropriate measure for egg survival after cryopreservation and frozen eggs have similar developmental potential as fresh eggs if they are frozen with an optimized method.

Intra-age, intercenter, and intercycle differences in chromosome abnormalities in oocytes

OBJECTIVE

To determine the extent of intra-age and intercycle variations in the frequency of first polar body aneuploidy in two consecutive cycles of oocyte retrieval undertaken by the same patient within 1 year.

DESIGN

Retrospective study.

SETTING

Fertility centers.

PATIENT(S)

Infertile couples undergoing IVF.

INTERVENTION(S)

Patients underwent two consecutive cycles of preimplantation genetic screening through first polar body biopsy within 1 year.

MAIN OUTCOME MEASURE(S)

Meiosis I aneuploidy.

RESULT(S)

A total of 226 patients underwent 452 cycles of preimplantation genetic screening. Differences within age groups were wide, with 0-100% of oocytes being chromosomally normal in all age groups. Euploidy rates between centers were significantly different (48% vs. 25%). Intercycle differences for the same patient were also wide (0-100%), but with 68.5% of patients having less than ±2 euploid eggs of difference between cycles.

CONCLUSION(S)

Although euploidy rate decreased on average with advancing maternal age, the high intra-age and intercenter variation in oocyte chromosome abnormalities emphasize the difficulty in estimating how many euploid oocytes a specific woman will have. This may have repercussions for fertility preservation where a defined number of eggs are currently frozen just based on maternal age.

Nanoliter droplet vitrification for oocyte cryopreservation

AIM

Oocyte cryopreservation remains largely experimental, with live birth rates of only 2-4% per thawed oocyte. In this study, we present a nanoliter droplet technology for oocyte vitrification.

MATERIALS & METHODS

An ejector-based droplet vitrification system was designed to continuously cryopreserve oocytes in nanoliter droplets. Oocyte survival rates, morphologies and parthenogenetic development after each vitrification step were assessed in comparison with fresh oocytes.

RESULTS

Oocytes were retrieved after cryoprotectant agent loading/unloading, and nanoliter droplet encapsulation showed comparable survival rates to fresh oocytes after 24 h in culture. Also, oocytes recovered after vitrification/thawing showed similar morphologies to those of fresh oocytes. Additionally, the rate of oocyte parthenogenetic activation after nanoliter droplet encapsulation was comparable with that observed for fresh oocytes. This nanoliter droplet technology enables the vitrification of oocytes at higher cooling and warming rates using lower cryoprotectant agent levels (i.e., 1.4 M ethylene glycol, 1.1 M dimethyl sulfoxide and 1 M sucrose), thus making it a potential technology to improve oocyte cryopreservation outcomes.

Current results with slow freezing and vitrification of the human oocyte

The past decade has witnessed renewed interest in human oocyte cryopreservation (OCP). This article reviews the two general methods used for OCP, slow freezing and vitrification, compares the outcomes associated with each technique and discusses the factors that might influence success with OCP (such as oocyte selection or day of transfer). Based on available data, OCP offers a reliable, reproducible method for preservation of the female gamete and will find increasing application in assisted reproductive technology. Oocyte cryopreservation can provide a number of advantages to couples undergoing assisted reproduction or to women interested in fertility preservation. Two methods, slow freezing and vitrification, have been used successfully for oocyte cryopreservation. This article reviews and compares these methods, and discusses various factors that can impact upon success of oocyte cryopreservation.

Use of cryo-banked oocytes in an ovum donation programme: a prospective, randomized, controlled, clinical trial

BACKGROUND

An efficient oocyte cryopreservation method is mandatory to establish a successful egg-banking programme. Although there are increasing reports showing good clinical outcomes after oocyte cryopreservation, there is still a lack of large controlled studies evaluating the effectiveness of oocyte cryo-banking. In this study, we aimed to compare the outcome of vitrified-banked oocytes with the gold standard procedure of employing fresh oocytes.

METHODS

A randomized, prospective, triple-blind, single-centre, parallel-group controlled-clinical trial (NCT00785993), including 600 recipients (alpha = 0.05 and power of 80% for sample-size calculation) selected among 1032 eligible patients from November 2008 to September 2009, was designed to compare the outcome of vitrified-banked oocytes with the gold standard procedure of employing fresh oocytes. The study was designed to establish the superiority of the ongoing pregnancy rate (OPR) of fresh oocytes over that of vitrified oocytes, by performing a likelihood ratio test in a logistic regression analysis expressed as odds ratio (OR) with 95% confidence interval (CI). A limit of 0.66 for OR of vitrified versus fresh groups was defined to set up a possible conversion from superiority to non-inferiority. Randomization was performed 1:1 based on a computer randomization list in vitrification (n = 300) or fresh groups (n = 300). The primary end-point was the OPR per randomized patient i.e. intention-to-treat population (ITT). Secondary end-points were clinical pregnancy (CPR), implantation (IR) and fertilization rates, respectively. Additionally, embryo developmental characteristics were recorded.

RESULTS

There were no differences in donor ovarian stimulation parameters, demographic baseline characteristics for donors and recipients, ovum donation indications or male factor distribution between groups (NS). The OPR per ITT was 43.7 and 41.7% in the vitrification and fresh groups, respectively. The OR of OPR was 0.921 in favour of the vitrification group. Nevertheless, the 95% CI was 0.667-1.274, thus the superiority of fresh group with respect to OPR was not proven (P = 0.744). Non-inferiority of the vitrified group compared with the fresh group was shown with a margin of 0.667, which was above the pre-established non-inferiority limit of 0.66. CPR per cycle (50.2 versus 49.8%; P = 0.933) or per embryo-transfer (55.4 versus 55.6% ; P = 0.974), and IR (39.9 versus 40.9%; P = 0.745) were similar for patients receiving either vitrified or fresh oocytes. The proportion of top-quality embryos obtained either by inseminated oocyte (30.8 versus 30.8% for Day-2; and 36.1 versus 37.7% for Day-3, respectively) or by cleaved embryos (43.6 versus 43.8% for Day-2 and 58.4 versus 60.7% for Day-3, respectively) was similar between groups (NS).

CONCLUSIONS

This controlled-randomized, clinical trial confirmed the effectiveness of oocyte cryo-storage in an ovum donation programme, failing to demonstrate the superiority of using fresh oocytes with respect to the use of vitrified egg-banked ones in terms of OPR. Instead, the non-inferiority of vitrified oocytes was confirmed. These findings involve highly relevant issues that may open a new range of possibilities in ART.

Application of intra- and extracellular sugars and dimethylsulfoxide to human oocyte cryopreservation

PURPOSE

Oocyte cryopreservation may avoid many complications of human embryo freezing and provide future fertility for women undergoing cancer therapy. The objective of this study was to explore the application of intra- and extracellular sugars in combination with small amounts of dimethylsulfoxide (DMSO) to human oocyte cryopreservation as an alternative approach.

METHODS

Discarded human oocytes that were obtained from IVF patients under informed consent and IRB approval, were cryopreserved by slow cooling to -196 degrees C after being randomly distributed into three groups: (i) DMSO control without intra- and extracellular sugar; (ii) extracellular sugar (raffinose) + DMSO; and (iii) intra- and extracellular sugar (trehalose and raffinose, respectively) + DMSO. Subsequently, all cryopreserved oocytes were thawed rapidly, and their survival was assessed by morphological criteria after 24 h of culture.

RESULTS

A total of 71 oocytes were evaluated in three groups with survival rates of 88.5% (23/26), 68.2% (15/22), and 52.2% (12/23) for intra- and extracellular sugar+DMSO, extracellular sugar+DMSO, and DMSO control groups, respectively.

CONCLUSION

These results support the use of intra- and extracellular sugars as an alternative approach for cryopreservation of human oocytes.