Counselling on cryopreservation of pronucleated oocytes

Determining the Optimal Duration of Progesterone Supplementation prior to Transfer of Cryopreserved Embryos and Its Impact on Implantation and Pregnancy Rates: A Pilot Study

Objective. To determine the optimal duration of progesterone supplementation prior to transfer of cryopreserved embryos and its impact on implantation and pregnancy rates. Study Design. Prospective randomised study. Materials and Methods. In an IVF unit of a tertiary centre, sixty-six patients undergoing cryopreserved embryo transfer cycles were included. Endometrial preparation was done with estradiol valerate. Once it reached a minimum of 7 mm, patients were allocated randomly into group I (n = 39) and group II (n = 27). Injectable progesterone 100 mg daily was then started for 3 and 4 days, respectively. This was followed by transfer of at least one thawed cleavage stage day 2 embryo of good quality. Groups I and II were compared in terms of clinical pregnancy and implantation rates. Results. In group I (3-day progesterone) and group II (4-day progesterone) the pregnancy rates were 41.02% (16/39) and 18.51% (5/27), respectively. On the other hand, the implantation rates were 16.82% (18/107) and 7.69% (6/78), respectively. The difference was statistically significant (p values 0.0172 and 0.0386, resp.). Conclusion. Progesterone supplementation for three days before the transfer of cleavage stage (day 2) cryopreserved embryos has significantly higher pregnancy and implantation rates, as compared to four-day supplementation.

A critical appraisal of cryopreservation (slow cooling versus vitrification) of human oocytes and embryos

BACKGROUND

Vitrification is now a commonly applied technique for cryopreservation in assisted reproductive technology (ART) replacing, in many cases, conventional slow cooling methodology. This review examines evidence relevant to comparison of the two approaches applied to human oocytes and embryos at different developmental stages.

METHODS

Critical review of the published literature using PubMed with particular emphasis on studies which include data on survival and implantation rates, data from fresh control groups and evaluation of the two approaches in a single setting.

RESULTS

Slow cooling is associated with lower survival rates and compromised development relative to vitrification when applied to metaphase II (MII) oocytes, although the vitrification results have predominantly been obtained using direct contact with liquid nitrogen and there is some evidence that optimal protocols for slow cooling of MII oocytes are yet to be established. There are no prospective randomized controlled trials (RCTs) which support the use of either technique with pronuclear oocytes although vitrification has become the method of choice. Optimal slow cooling, using modifications of traditional methodology, and vitrification can result in high survival rates of early embryos, which implant at the same rate as equivalent fresh counterparts. Many studies report high survival and implantation rates following vitrification of blastocysts. Although slow cooling of blastocysts has been reported to be inferior in some studies, others comparing the two approaches in the same clinical setting have demonstrated comparable results. The variation in the extent of embryo selection applied in studies can lead to apparent differences in clinical efficiency, which may not be significant if expressed on a 'per oocyte used' basis.

CONCLUSIONS

Available evidence suggests that vitrification is the current method of choice when cryopreserving MII oocytes. Early cleavage stage embryos can be cryopreserved with equal success using slow cooling and vitrification. Successful blastocyst cryopreservation may be more consistently achieved with vitrification but optimal slow cooling can produce similar results. There are key limitations associated with the available evidence base, including a paucity of RCTs, limited reporting of live birth outcomes and limited reporting of detail which would allow assessment of the impact of differences in female age. While vitrification has a clear role in ART, we support continued research to establish optimal slow cooling methods which may assist in alleviating concerns over safety issues, such as storage, transport and the use of very high cryoprotectant concentrations.

Slow freezing, vitrification and ultra-rapid freezing of human embryos: a systematic review and meta-analysis

Embryo cryopreservation is an important aspect of assisted reproduction. Many methods have been described, but they have been poorly investigated in randomized trials, highlighting the need for a systematic review of the literature. Meticulous electronic/hand searches were performed to locate randomized trials (RCT) comparing embryo cryopreservation methods. Primary outcomes were clinical pregnancy rate (CPR) and incidence of congenital abnormalities. Secondary outcomes included live-birth (LBR), ongoing pregnancy (OPR), implantation (IR), and miscarriage (MR) rates. Data were extracted to allow for an intention-to-treat analysis and analysed using a random-effects model. Literature search revealed 11 RCT, of which five were excluded. The quality of the included studies was variable, but generally poor. There was a significantly higher CPR, OPR and IR with vitrification compared with slow freezing (odds ratio (OR)=1.55, 95% confidence interval (CI)=1.03-2.32, OR=1.82, 95% CI=1.04-3.20 and OR=1.49, 95% CI=1.03-2.15, respectively). In addition, there was a significantly lower CPR and OPR with embryo ultra-rapid freezing compared with slow freezing (OR=0.35, 95% CI=0.16-0.76 and OR=0.37, 95% CI=0.17-0.81, respectively). Vitrification is superior to slow freezing, which in turn is superior to ultra-rapid freezing. However, more well-designed and powered studies are needed to further corroborate these findings.

Clinical efficiency of oocyte and embryo cryopreservation

The assessment of the standard for success of in vitro fertilization (IVF) treatment is an arduous task. Clinical efficiency and safety of a given procedure should represent fundamental tools for objective comparison. However, differences in patient populations, laboratory protocols, and expression of clinical data make the analysis of different studies and strategies very difficult. Formulation of the standard for success through the cumulative delivery rate per cycle of stimulation is a very attractive option because it includes the essential contribution of frozen embryos, which can represent 30-40% of all deliveries, while taking into account the need to minimize the proportion of pharmacological and surgical treatments. Embryo cryopreservation may be applied at different postinsemination stages. Larger and more detailed sets of data are available for day 2 embryo freezing, which allows cumulative delivery rates of 50-60% in good prognosis patients. In the last few years, novel freezing methods have improved the overall efficiency of oocyte cryopreservation. Especially in contexts afflicted by legal restrictions to embryo cryo- preservation, this form of preservation has started to have an impact on the IVF standard of success, generating cumulative pregnancy rates approaching 50%. Despite having been applied systematically by some IVF programs for only a few years, oocyte freezing already competes in efficiency with pronuclear-stage cryopreservation, and it does not appear unrealistic to predict that in the future it will challenge the dominance of embryo cryopreservation as the preferred form of conservation.

Evidence-based clinical outcome of oocyte slow cooling

In the last few years, there has been a significant improvement in oocyte cryopreservation techniques. To investigate the clinical significance of oocyte freezing, an assessment of the cumulative pregnancy rate per started cycle derived from the use of fresh and frozen-thawed oocytes was performed. Between 2004 and 2006, 749 cycles were carried out, in which no more than three fresh oocytes were inseminated either by standard IVF or microinjection. Supernumerary mature oocytes were cryopreserved by slow cooling. Cryopreservation of fresh embryos was performed in rare cases to prevent the risk of ovarian hyperstimulation syndrome using a standard embryo freezing protocol. Fresh embryo transfer cycles totalled 680, 257 of which resulted in pregnancy. The pregnancy rates per patient and per transfer were 34.3% and 37.8% respectively. When frozen-thawed oocytes were used, following 660 thawing cycles, 590 embryo transfers were performed in 510 patients. Eighty-eight pregnancies were achieved with embryos from frozen oocytes, with a success rate of 17.2% per cycle. When fresh and frozen-thawed cycles were combined, the number of pregnancies was 355, giving a cumulative pregnancy rate of 47.4%. Oocyte cryopreservation can contribute considerably to the overall clinical success, ensuring a cumulative rate approaching that achievable with embryo storage.

Three years of routine vitrification of human zygotes: is it still fair to advocate slow-rate freezing?

Cryopreservation of human oocytes and embryos is a necessary tool in assisted reproduction treatment that leads to an increased cumulative outcome while decreasing costs. Vitrification is a cryopreservation technique that leads to a glass-like solidification, with rapid cooling of cells or tissues. Nowadays vitrification is claimed to be the future of cryopreservation of human embryos due to improved survival rates and clinical outcomes. This study was conducted at a university clinic to assess the safety and efficiency of vitrification of human zygotes as a routine procedure. A total of 849 pronuclear-stage (PN) zygotes were vitrified between March 2004 and July 2006. During this period, 103 cycles of cryopreserved embryo transfer were completed. In total, 339 PN zygotes were thawed resulting in an 89% survival rate (302 PN zygotes). The mean number of embryos per transfer was 2.2. The pregnancy rate obtained was three times higher (36.9%) than that obtained with the slow-rate freezing method (10.2%) used previously in the same centre. In conclusion, vitrification of human zygotes at the pronuclear stage seems to be a successful and reliable method with favourable outcomes and can be recommended as a routine technique for cryopreservation of human embryos.

What is the ‘ideal’ duration of progesterone supplementation before the transfer of cryopreserved–thawed embryos in estrogen/progesterone replacement protocols?

Different studies dealing with the start of progesterone supplementation in assisted reproduction treatment cycles have shown that the problem apparently is the correct timing. We therefore would like to discuss the data on: (i) the start of progesterone replacement in oocyte donation programmes; (ii) the start of progesterone replacement in frozen-thawed hormone-supplemented cycles; (ii) the problem of too early a rise of progesterone in fresh IVF cycles as a model of too early an administration of progesterone; and (iv) the benefit of high progesterone levels on the day of embryo transfer in fresh IVF cycles. From the data reviewed in this paper it seems to be appropriate to start progesterone administration before transfer in oocyte donation programmes as well as transfer of cryopreserved/thawed cells as soon as the endometrium is developed sufficiently (> or =8 mm, trilaminar pattern), and to perform the embryo transfer not before day 3-4 of progesterone treatment, i.e. embryo development on day 2-3. Studies dealing with the influence of too early a rise of progesterone in fresh IVF cycles have shown different results. In fact high progesterone levels seem to reflect a high response but not a lower probability of conception. Furthermore, high progesterone levels on the day of embryo transfer in fresh IVF cycles could lower myometrial contractility and therefore increase implantation rates. Since the experience from oocyte donation programes shows the benefit of a longer preparation time using progesterone, and high progesterone levels seem to have a benefit during embryo transfer, this would suggest extending progesterone administration before transfer. However, we have to find the optimal individual transfer protocol after mock cycles, for example with pinopode detection or other methods applicable in routine IVF programmes. We need more studies to be sure whether reproductive outcome after transfer of cryopreserved-thawed cells in estrogen/progesterone supplement cycles is influenced by the duration of progesterone pretreatment. If this is so, we must look for practicable methods to modify the protocols according to the individual patient, the embryonic developmental stage during transfer and other variables.

In-vitro maturation of germinal-vesicle oocytes and cryopreservation in metaphase I/II: a possible additional option to preserve fertility during ovarian tissue cryopreservation

This study describes the possibility of combining two options in order to preserve female fertility: cryopreservation of human ovarian tissue and in-vitro matured germinal vesicle (GV) oocytes retrieved during tissue dissection. In contrast to ovarian tissue cryopreservation, the cryostorage of in-vitro matured unfertilized metaphaseI/II oocytes could be a more realistic option. This concept of preserving fertility before chemotherapy and/or radiotherapy without a long time delay could be an additional reason for favouring ovarian tissue cryopreservation. This concept is discussed in regard to two cases.

Cumulative pregnancy rates and drop-out rates in a German IVF programme: 4102 cycles in 2130 patients

Cumulative pregnancy rates are useful in counselling couples on their chance of conceiving during infertility treatment. Patients also have to be counselled about the physical and psychological stress of infertility treatment. Beside the pregnancy rates, drop-out rates are a direct, and may be the most important, marker of physician quality in an IVF programme. Data from 4102 IVF cycles in 2130 patients in Germany were analysed retrospectively. Data were analysed using descriptive statistics as well as the Kaplan-Meier procedure. A real cumulative pregnancy rate of 31.2% was achieved after four cycles with an expected cumulative pregnancy rate (ECPR) of 53.3%. Age was a significant factor regarding pregnancy rates (ECPR after four cycles: 57.1% <35 years, 44.8% > or =35 years, 35.4% > or =40 years). The drop-out rate of non-pregnant patients increased from 39.9% after the first cycle to 62.2% after the fourth cycle, indicating the enormous stress and frustration that increased during the course of treatment. The drop-out rate should be used as an important marker of quality control. The presented data give, for the first time, a good basis for this counselling procedure in Germany.

Recent developments in human oocyte, embryo and blastocyst vitrification: where are we now?

The target of any cryopreservation procedure should be to ensure high survival rates of living cells after thawing. Two important parameters determine the success of any cryopreservation protocol: the manner in which cells regain equilibrium in response to cooling, and the speed of freezing (cooling rate). Slow-rate freezing protocols result in the formation of ice crystals during cooling and warming. Vitrification, in which high cooling rates in combination with a high concentration of cryoprotectant are used, does not produce any ice crystals during cooling and warming. However, there is a practical limit to the attainable cooling speed, and also a biological limit to the concentration of cryoprotectant tolerated by the cells during vitrification. Although post-warming survival depends on the species, the developmental stage and the quality of the embryos being vitrified, it seems clear that vitrification methods are increasingly successful and might be a better method than slow cooling procedures in the field of cryobiology. Many of the potential problems and benefits underlying vitrification as a method of choice for embryo cryopreservation in clinical embryology will be discussed in this review.