Cryopreservation of human embryos at the pronucleate, early cleavage, or expanded blastocyst stages

Double vitrification and warming does not compromise the chance of live birth after single unbiopsied blastocyst transfer

STUDY QUESTION

Does double vitrification and thawing of an embryo compromise the chance of live birth after a single blastocyst transfer?

SUMMARY ANSWER

The live birth rate (LBR) obtained after double vitrification was comparable to that obtained after single vitrification.

WHAT IS KNOWN ALREADY

Double vitrification-warming (DVW) is commonly practiced to accommodate surplus viable embryos suitable for transfer, to allow retesting of inconclusively diagnosed blastocysts in preimplantation genetic testing (PGT), and to circumvent limitations associated with national policies on embryo culture in certain countries. Despite its popularity, the evidence concerning the impact of DVW practice on ART outcomes is limited and lacking credibility. This is the first thorough investigation of clinical pregnancy and LBR following DVW in the case where the first round of vitrification occurred at the zygote stage and the second round occurred at the blastocyst stage in the absence of biopsy.

STUDY DESIGN SIZE DURATION

This is a retrospective observational analysis of n = 407 single blastocyst transfers whereby embryos created by IVF/ICSI were vitrified-warmed once (single vitrification-warming (SVW) n = 310) or twice (DVW, n = 97) between January 2017 and December 2021.

PARTICIPANTS/MATERIALS SETTING METHODS

In the SVW group, blastocysts were vitrified on Day 5/6 and warmed on the day of embryo transfer (ET). In the DVW group, two pronuclear (2PN) zygotes were first vitrified-warmed and then re-vitrified on Day 5/6 and warmed on the day of ET. Exclusion criteria were ETs from PGT and vitrified-warmed oocyte cycles. All of the ETs were single blastocyst transfers performed at the University Hospital Zurich in Switzerland following natural or artificial endometrial preparation.

MAIN RESULTS AND THE ROLE OF CHANCE

The biochemical pregnancy rate, clinical pregnancy rate (CPR), and LBR were all comparable between the DVW and SVW groups. The CPR for DVW was 44.3% and for SVW it was 42.3% (P = 0.719). The LBR for DVW was 30.9% and for SVW it was 28.7% (P = 0.675). The miscarriage rate was additionally similar between the groups: 27.9% for DVW and 32.1% for SVW groups (P = 0.765).

LIMITATIONS REASONS FOR CAUTION

The study is limited by its retrospective nature. Caution should be taken concerning interpretation of these findings in cases where DVW occurs at different stages of embryo development.

WIDER IMPLICATIONS OF THE FINDINGS

The result of the present study on DVW procedure provides a framework for counselling couples on their chance of clinical pregnancy per warming cycle. It additionally provides confidence and reassurance to laboratory professionals in certain countries where national policies limit embryo culture strategies making DVW inevitable.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the University Research Priority Program 'Human Reproduction Reloaded' of the University of Zurich. The authors have no conflict of interest related to this study to declare.

TRIAL REGISTRATION NUMBER

N/A.

The impact of zygote vitrification timing on pregnancy rate in frozen-thawed IVF/ICSI cycles

Introduction: Cryopreservation of bipronuclear (2PN) stage zygotes is an integral part of IVF laboratory practice in countries with strict embryo culture legislation. Vitrification of zygotes is compatible with several strategies in infertility treatments holding a freeze-all indication and allows for effective workload management in settings with limited resources. Although it yields high survival rates and clinical outcomes, the ideal timing to commence vitrification of zygotes is elusive while it is empirically practiced in the window between 17 and 21 h post-insemination (hpi). We aimed to deduce the association between pregnancy rate and the time interval from insemination (IVF and ICSI) to vitrification to contribute to the standardization ofzygote cryopreservation. Methods: A retrospective analysis of data on vitrification timings and pregnancy outcomes collected between 2011 and 2019 was performed. All included women received an embryo transfer after warming of vitrified zygotes at the 2PN stage. Results: A total of 468 embryo transfers were included of which 182 (38.9%) resulted in pregnancy and 286 (61.1%) not. Vitrification was on average performed 18.74 ±0.63 hpi in the pregnant group and 18.62 ± 0.64 hpi in the non-pregnant group (OR 1.36, 95% CI 1.01; 1.83, p = 0.045). A multivariate analysis controlling for uterine pathologies, maternal age, AMH, the number of MII oocytes, previous history of pregnancy success, endometriosis, AFC, nicotine intake and male factor infertility showed no predictive value of vitrification timing on pregnancy rate. Three time intervals between insemination and vitrification were defined: 17:00 to 18:00 hpi (Group A), 18:01 to 19:00 hpi (Group B) and 19:01 to 21:00 hpi (Group C). Pregnancy occurred in 40/130 women (30.80%) in Group A, in 115/281 women (40.90%) in Group B and in 27/57 women (47.40%) in Group C. Univariate but not multivariate analysis showed a significantly higher pregnancy rate after the latest time interval between insemination and 2PN vitrification when compared to the earliest (Group C vs. A, OR 2.03, 95% CI 1.07; 3.84, p = 0.031). Discussion: These findings encourage further investigation on the impact of vitrification timing on clinical outcomes and hold the potential to standardize cryopreservation of zygotes from IVF/ICSI cycles to eventually improve the quality of long-term ART outcomes.

A comparison of frozen-thawed embryo transfer protocols in 2920 single-blastocyst transfers

OBJECTIVE

To assess the effect of frozen-thawed embryo transfer (FET) protocol on live-birth rate (LBR) and clinical pregnancy rate (CPR), in single-vitrified-blastocyst transfer MATERIALS AND METHODS: Retrospective cohort study with FET of a single-blastocyst embryos (n = 2920 cycles) thawed 2013-2018. FET protocols were natural cycles (NC-FET) (n = 147), artificial hormone replacement treatment cycles (HRT-FET) (n = 2645), and modified NC (mNC) with hCG triggering (n = 128). Primary outcome was LBR. Adjustment for age, embryo grade, year of freezing\thawing, infertility cause, and endometrial thickness was performed.

RESULTS

There were no significant differences between the groups with regard to female age, embryo grade, and endometrial thickness. LBR was higher in the mNC compared to HRT-FET cycles (38.3% vs. 20.9% P < 0.0001), and in the NC compared to HRT-FET cycles (34.7% vs. 20.9%, P = 0.0002). CPR was higher in the mNC compared to HRT-FET cycles (46.1% vs. 33.3% P = 0.0003), and in the NC compared to HRT-FET cycles (45.9% vs. 33.3%, P = 0.002). There was no significant difference in LBR or CPR between NC-FET and mNC-FET. Higher LBR with NC-FET and mNC-FET remained significant after adjusting for confounders (aOR 2.42, 95%CI 1.53-3.66, P < 0.0001).

CONCLUSION

The use of the convenient artificial HRT-FET cycles must be cautiously reconsidered in light of the potential negative effect on LBR when compared with natural cycle FET.

Hollow fiber vitrification allows cryopreservation of embryos with compromised cryotolerance

PURPOSE

This study aims to demonstrate vitrification methods that provide reliable cryopreservation for embryos with compromised cryotolerance.

METHODS

Two-cell stage mouse embryos and in vitro produced porcine embryos were vitrified using the hollow fiber vitrification (HFV) and Cryotop (CT) methods. The performance of these two methods was compared by the viability of the vitrified-rewarmed embryos.

RESULTS

Regardless of the method used, 100% of the mouse 2-cell embryos developed successfully after vitrification-rewarming into the blastocyst stage, whereas vitrification tests using porcine morulae with the HFV method produced significantly better results. The developmental rates of vitrified porcine morula into the blastocyst stage, as well as blastocyst cell number, were 90.3% and 112.3 ± 6.9 in the HFV group compared with 63.4% and 89.5 ± 8.1 in the CT group (P < .05). Vitrification tests using 4- to 8-cell porcine embryos resulted in development into the blastocyst stage (45.5%) in the HFV group alone, demonstrating its better efficacy. The HFV method did not impair embryo viability, even after spontaneous rewarming at room temperature for vitrified embryos, which is generally considered a contraindication.

CONCLUSION

Vitrification test using embryos with compromised cryotolerance allows for more precise determining of effective cryopreservation methods and devices.

Cycle regimens for frozen-thawed embryo transfer

BACKGROUND

Among subfertile couples undergoing assisted reproductive technology (ART), pregnancy rates following frozen-thawed embryo transfer (FET) treatment cycles have historically been found to be lower than following embryo transfer undertaken two to five days following oocyte retrieval. Nevertheless, FET increases the cumulative pregnancy rate, reduces cost, is relatively simple to undertake and can be accomplished in a shorter time period than repeated in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI) cycles with fresh embryo transfer. FET is performed using different cycle regimens: spontaneous ovulatory (natural) cycles; cycles in which the endometrium is artificially prepared by oestrogen and progesterone hormones, commonly known as hormone therapy (HT) FET cycles; and cycles in which ovulation is induced by drugs (ovulation induction FET cycles). HT can be used with or without a gonadotrophin releasing hormone agonist (GnRHa). This is an update of a Cochrane review; the first version was published in 2008.

OBJECTIVES

To compare the effectiveness and safety of natural cycle FET, HT cycle FET and ovulation induction cycle FET, and compare subtypes of these regimens.

SEARCH METHODS

On 13 December 2016 we searched databases including Cochrane Gynaecology and Fertility's Specialised Register, CENTRAL, MEDLINE, Embase, PsycINFO and CINAHL. Other search sources were trials registers and reference lists of included studies.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) comparing the various cycle regimens and different methods used to prepare the endometrium during FET.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures recommended by Cochrane. Our primary outcomes were live birth rates and miscarriage.

MAIN RESULTS

We included 18 RCTs comparing different cycle regimens for FET in 3815 women. The quality of the evidence was low or very low. The main limitations were failure to report important clinical outcomes, poor reporting of study methods and imprecision due to low event rates. We found no data specific to non-ovulatory women. 1. Natural cycle FET comparisons Natural cycle FET versus HT FETNo study reported live birth rates, miscarriage or ongoing pregnancy.There was no evidence of a difference in multiple pregnancy rates between women in natural cycles and those in HT FET cycle (odds ratio (OR) 2.48, 95% confidence interval (CI) 0.09 to 68.14, 1 RCT, n = 21, very low-quality evidence). Natural cycle FET versus HT plus GnRHa suppressionThere was no evidence of a difference in rates of live birth (OR 0.77, 95% CI 0.39 to 1.53, 1 RCT, n = 159, low-quality evidence) or multiple pregnancy (OR 0.58, 95% CI 0.13 to 2.50, 1 RCT, n = 159, low-quality evidence) between women who had natural cycle FET and those who had HT FET cycles with GnRHa suppression. No study reported miscarriage or ongoing pregnancy. Natural cycle FET versus modified natural cycle FET (human chorionic gonadotrophin (HCG) trigger)There was no evidence of a difference in rates of live birth (OR 0.55, 95% CI 0.16 to 1.93, 1 RCT, n = 60, very low-quality evidence) or miscarriage (OR 0.20, 95% CI 0.01 to 4.13, 1 RCT, n = 168, very low-quality evidence) between women in natural cycles and women in natural cycles with HCG trigger. However, very low-quality evidence suggested that women in natural cycles (without HCG trigger) may have higher ongoing pregnancy rates (OR 2.44, 95% CI 1.03 to 5.76, 1 RCT, n = 168). There were no data on multiple pregnancy. 2. Modified natural cycle FET comparisons Modified natural cycle FET (HCG trigger) versus HT FETThere was no evidence of a difference in rates of live birth (OR 1.34, 95% CI 0.88 to 2.05, 1 RCT, n = 959, low-quality evidence) or ongoing pregnancy (OR 1.21, 95% CI 0.80 to 1.83, 1 RCT, n = 959, low-quality evidence) between women in modified natural cycles and those who received HT. There were no data on miscarriage or multiple pregnancy. Modified natural cycle FET (HCG trigger) versus HT plus GnRHa suppressionThere was no evidence of a difference between the two groups in rates of live birth (OR 1.11, 95% CI 0.66 to 1.87, 1 RCT, n = 236, low-quality evidence) or miscarriage (OR 0.74, 95% CI 0.25 to 2.19, 1 RCT, n = 236, low-quality evidence) rates. There were no data on ongoing pregnancy or multiple pregnancy. 3. HT FET comparisons HT FET versus HT plus GnRHa suppressionHT alone was associated with a lower live birth rate than HT with GnRHa suppression (OR 0.10, 95% CI 0.04 to 0.30, 1 RCT, n = 75, low-quality evidence). There was no evidence of a difference between the groups in either miscarriage (OR 0.64, 95% CI 0.37 to 1.12, 6 RCTs, n = 991, I² = 0%, low-quality evidence) or ongoing pregnancy (OR 1.72, 95% CI 0.61 to 4.85, 1 RCT, n = 106, very low-quality evidence).There were no data on multiple pregnancy. 4. Comparison of subtypes of ovulation induction FET Human menopausal gonadotrophin(HMG) versus clomiphene plus HMG HMG alone was associated with a higher live birth rate than clomiphene combined with HMG (OR 2.49, 95% CI 1.07 to 5.80, 1 RCT, n = 209, very low-quality evidence). There was no evidence of a difference between the groups in either miscarriage (OR 1.33, 95% CI 0.35 to 5.09,1 RCT, n = 209, very low-quality evidence) or multiple pregnancy (OR 1.41, 95% CI 0.31 to 6.48, 1 RCT, n = 209, very low-quality evidence).There were no data on ongoing pregnancy.

AUTHORS' CONCLUSIONS

This review did not find sufficient evidence to support the use of one cycle regimen in preference to another in preparation for FET in subfertile women with regular ovulatory cycles. The most common modalities for FET are natural cycle with or without HCG trigger or endometrial preparation with HT, with or without GnRHa suppression. We identified only four direct comparisons of these two modalities and there was insufficient evidence to support the use of either one in preference to the other.

Vitrification of oocytes, embryos and blastocysts

In assisted reproductive technology, cryopreservation of human oocytes and embryos has been significantly improved by refined slow-cooling and the new vitrification method. The slow-cooling method requires a programmed cryo-machine, and usually takes several hours. It is, however, difficult to eliminate injuries resulting from ice formation completely. Vitrification has become a reliable strategy because it is simple, can lead to high survival rates and viability, and has better clinical outcome. Vitrification transforms cells into an amorphous glassy state inside and outside the vitrified cell with ultra-rapid cooling and warming steps by plunging the oocytes and embryos into liquid nitrogen, instead of ice-crystal formation. Over the past decade, several advances in vitrification technologies have improved clinical efficiency and outcome. In this chapter, we focus on vitrification technologies for cryopreservation in human assisted reproductive technology.

Comparing thaw survival, implantation and live birth rates from cryopreserved zygotes, embryos and blastocysts

CONTEXT:

Most in vitro fertilization (IVF) programs employ embryo cryopreservation to enhance pregnancies from a single ovarian stimulation. More embryos are created, some of which are not transferred to the uterus immediately, generating a need for improved cryopreservation protocols. One protocol may involve growing embryos to a further stage of development, allowing only embryos with proven developmental capabilities to be cryopreserved. Here we examined thaw survival, implantation and live birth rates of embryos cryopreserved at different stages.

AIMS:

We examined thaw survival, implantation and live birth rates of embryos cryopreserved at the zygote, day 3 (D3) embryos or blastocyst stage.

SETTINGS AND DESIGN:

This is a retrospective study from a single academic IVF program.

PATIENTS AND METHODS:

A retrospective study of all patients who had frozen embryos transferred to their uteri from year 2002 to 2008 at a single academic IVF program was conducted.

STATISTICAL ANALYSIS USED:

Analysis of variance followed by Fisher's Exact Test was performed to compare the survival after thaw, implantation and live birth rates between the three groups.

RESULTS:

One thousand nine hundred and ninety-one zygotes, 2880 D3 embryos and 503 blastocysts were frozen using a slow freeze technique, thawed and transferred. Significantly more D3 embryos and blastocysts survived the thawing process compared to zygotes and significantly higher implantation rate per number of thawed blastocysts was achieved than that for zygotes. Live birth rates were similar between the three groups.

CONCLUSIONS:

Growing embryos to blastocyst stage prior to cryopreservation is associated with fewer frozen embryos but does not appear compromise patients’ chance of achieving pregnancy

Embryo cryopreservation

Embryo cryopreservation is a well established technique and is used widely for embryo banking of genetically valuable strains of mice, the transport and proliferation of farm animals and as a valuable adjunct to human in vitro fertilization (IVF). The range of methods presently used to cryopreserve human embryos has been recently reviewed. This article examines the results obtained by the established freezing techniques and developments in the new rapid cooling methods. There is a dramatic contrast in the simplicity, ease and cost between these new rapid techniques and the conventional slow cooling or equilibrium freezing methods and it is likely that the rapid freezing will replace conventional freezing by slow cooling which is presently in widespread use in IVF clinics.

Current aspects of blastocyst cryopreservation

Cryopreservation of human gametes and embryos has become an essential part of assisted reproduction. Successful cryopreservation of human blastocysts is increasingly relevant as extended in-vitro culture of human embryos becomes more common, permitting routine use of blastocyst transfer in IVF programmes. This reduces the number of embryos transferred, thereby reducing multiple pregnancies and maximizing cumulative pregnancy rates per oocyte retrieval. The superiority of blastocyst freezing over earlier stage freezing in terms of implantation per thawed embryo transferred improves overall expectations for the cryopreservation programme. Therefore, a reliable procedure for the cryopreservation of blastocysts is needed because, after transfer, only a small number of supernumerary blastocysts are likely to be available for cryopreservation. Since the early 1980s, two common techniques have been used in cryopreservation: the conventional slow cooling method and the more recent rapid procedure known as vitrification. Vitrification has become an attractive alternative to slow freezing, since it appears to result in significantly higher survival and pregnancy rates. The aim of this review is to focus on the cryopreservation of human blastocysts using slow and rapid protocols and to assess the impact of the crypreservation protocol used on the survival, implantation and pregnancy rates.

Cycle regimens for frozen-thawed embryo transfer

BACKGROUND

Pregnancy rates following frozen-thawed embryo transfer (FET) treatment have always been found to be lower than following embryo transfer using fresh embryos. Nevertheless, FET increases the (cumulative) pregnancy rate, reduces cost, is relatively simple to undertake and can be accomplished in a shorter time period compared to repeated 'fresh' cycles. FET is performed using different cycle regimens: spontaneous ovulatory cycles, cycles in which ovulation is induced by drugs and cycles in which the endometrium is artificially prepared by oestrogen (O) and progesterone (P) hormones, with or without a gonadotrophin releasing hormone agonist (GnRHa).

OBJECTIVES

To determine whether there is a difference in outcome between natural cycle FET, artificial cycle FET and ovulation induction cycle FET.

SEARCH STRATEGY

Our search included CENTRAL,DARE, MEDLINE (1950 to 2007), EMBASE (1980 to 2007) and CINAHL (1982 to 2007).

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing the various cycle regimens and different methods used to prepare the endometrium during FET in assisted reproductive technology (ART).

DATA COLLECTION AND ANALYSIS

The two authors independently extracted data. Dichotomous outcomes results (e.g. clinical pregnancy rate) were expressed as an odds ratio (OR) with 95% confidence intervals (CI) for each study. Continuous outcome results (endometrial thickness) were expressed as weighted mean difference (WMD). Where suitable, results were combined for meta-analysis with RevMan software using the Peto-modified Mantel-Haenszel method.

MAIN RESULTS

Seven randomised controlled studies assessing six comparisons and including 1120 women in total were included in this review.1) O + P FET versus natural cycle FET: this comparison demonstrated no significant differences in outcomes but confidence intervals remain wide, and therefore moderate differences in either direction remain possible (OR 1.06, 95% CI 0.40 to 2.80, P 0.91).2) GnRHa + O + P FET versus O + P FET: this comparison showed that the live birth rate per woman was significantly higher in the former group (OR 0.38, 95% CI 0.17 to 0.84, P 0.02). The clinical pregnancy rate was also higher but not significantly so (OR 0.76, 95% CI 0.52 to 1.10, P 0.14).3) O + P FET versus follicle stimulating hormone (FSH) FET, 4) O + P FET versus clomiphene FET and 5) GnRHa + O + P FET versus clomiphene FET: there were no differences in the outcomes in the comparison of these cycle regimens.6) Clomiphene + human menopausal gonadotrophin (HMG) FET versus HMG FET: in a comparison of two ovulation induction regimes the pregnancy rate was found to be significantly higher in the HMG group (OR 0.46, 95% CI 0.23 to 0.92). There were also fewer cycle cancellations and a lower multiple pregnancy rate when HMG was used without clomiphene but these did not reach statistical significance.

AUTHORS' CONCLUSIONS

At the present time there is insufficient evidence to support the use of one intervention in preference to another.

Frozen-thawed embryo transfer and live birth: Long-term follow-up after one oocyte retrieval

Frozen-thawed embryos accounted for 39% (249 of 639) of live births from 931 consecutive first oocyte retrievals after median follow-up of 6.5 years with consistent use of pronuclear-stage freezing and cleavage-stage transfer. Survival after thaw was 95% (2,129 of 2,247). Implantation and live birth rates per individual frozen-thawed embryo transfered were 22% (431 of 1,937) and 18% (346 of 1,937), respectively.

Pregnancy rates after transfer of cryopreserved blastocysts cultured in a sequential media

OBJECTIVE

This study was undertaken to determine the pregnancy rate after transfer of cryopreserved blastocysts.

STUDY DESIGN

Retrospective review of 61 patients from January 1, 2002, to December 31, 2003, who were transferred with blastocyst embryos cryopreserved on day 5 or 6 after culture in a sequential media. The cryopreserved blastocysts were thawed by using a 7-step dilution process after rapid thawing half hour to 2 hours before embryo transfer.

RESULTS

The pregnancy rate after transfer of 61 patients with cryopreserved blastocysts was 66%, with 49% having cardiac activity. The pregnancy rate after transfer of 3 blastocysts was 71% and after transfer of 2 blastocysts was 66%. The pregnancy rate of blastocysts cryopreserved after intracytoplasmic sperm injection was 56%.

CONCLUSION

Cryopreservation and transfer of blastocysts appears to be a reliable procedure, and that the human blastocyst can be cryopreserved and thawed without a significant loss of viability.

Cryopreservation of human embryos at the morula stage and outcomes after transfer

OBJECTIVE

To evaluate the survival rate of human morula embryo freezing and the morphological alterations during freezing, during and after thawing, and their applications in embryo selection.

DESIGN

Retrospective observational study.

SETTING

Private infertility clinic.

PATIENT(S)

Consecutive patients under age 39 undergoing frozen morula embryo transfers from December 1999 to May 2003.

INTERVENTION(S)

Embryo freezing was performed at the morula stage. Embryo thaw and post-thaw ETs were conducted on the same day, which is equivalent to a day 4 ET.

MAIN OUTCOME MEASURE(S)

Morphological alterations during freezing and thawing and after thawing. Post-thaw embryo survival rates, transferable rates, pregnancy rates, and implantation rates.

RESULT(S)

Morula embryos showed reversed morphological alterations during the freezing process; these alterations were recovered during thawing or shortly after the thawing. Post-thaw survival rates showed no significant difference between any of the morula substages. However, embryos scored as grade 3, which represented good quality, had significantly higher post-thaw survival and transferable rates than grade 2 and 1 embryos. Patients who received at least one grade 3 embryo had significantly higher pregnancy rates, implantation rates, and ongoing/live birth rates than other groups.

CONCLUSION(S)

An acceptable survival rate can be achieved after cryopreservation of human morula embryos, and morphological alterations that occur during and shortly after an embryo thaw can be a feasible index for determining viable embryos.

Successful freezing and thawing of blastocysts cultured in sequential media using a modified method

OBJECTIVE

To evaluate the clinical role of blastocyst freezing and thawing after prolonged culturing in sequential media.

DESIGN

Retrospective analysis of 293 blastocyst freeze-thawing cycles.

SETTING

University hospital infertility unit.

PATIENT(S)

Nonselected couples undergoing IVF.

INTERVENTION(S)

Blastocysts were frozen and thawed by a modified method.

MAIN OUTCOME MEASURES

Blastocyst recovery after freeze-thawing and pregnancy rates after the transfer. Evaluation of the effect of the number of transferred blastocysts, the method of IVF, and of the woman's age on the results achieved by frozen-thawed blastocysts.

RESULT(S)

Frozen-thawed blastocysts provided a 29.5% clinical pregnancy rate per transfer. After the transfer of three blastocysts the pregnancy rate was 42.0%, and after the transfer of one or two blastocysts it was approximately the same (25.0% and 28.0%, respectively). The method of IVF did not affect pregnancy rates, but the increasing age of the woman did. Pregnancies were characterized by a low abortion rate (8.0%) regardless of the age of the woman.

CONCLUSION(S)

A modified method for blastocyst freeze-thawing provides good clinical results. It offers the possibility for a single-thawed blastocyst transfer and represents a good alternative for older women because of its lower risk of spontaneous abortion.

The added value of embryo cryopreservation to cumulative ongoing pregnancy rates per IVF treatment: is cryopreservation worth the effort?

PURPOSE

To calculate the added benefit of a cryopreservation program to the cumulative ongoing pregnancy rate over a maximum of three cycles of IVF.

METHODS

A total of 1251 couples beginning their first IVF treatment between January 1995 and December 1999 were evaluated. Ongoing pregnancies from fresh and subsequent cryopreserved embryo transfer cycles were analyzed. Pregnancies arising from the cryopreservation cycle were considered to augment the cumulative pregnancy rate when no ongoing pregnancy arose from the fresh embryo transfer cycle.

RESULTS

The ongoing pregnancy rate per cryopreserved embryo transfer was 11.7%. The cumulative ongoing pregnancy rate following three successive started fresh IVF cycles was 42.5%. When pregnancies arising from the transfer of thawed cryopreserved embryos were included, the cumulative ongoing pregnancy rate increased to 43.8%, rising to 44.8% when extrapolated data from as yet unthawed embryos was included.

CONCLUSIONS

When analyzed in these terms, the supplementary benefit of cryopreserving supranumerical embryos appears limited.

Human ovarian tissue cryopreservation: indications and feasibility

BACKGROUND

The cryopreservation of ovarian tissue may enable women exposed to gonadotoxic treatments to have children at a later date.

METHODS

Between April 1998 and October 2000, we evaluated the feasibility of long-term ovarian tissue cryopreservation in 51 women who were all at risk of becoming sterile following treatment.

RESULTS

Ovarian tissue was not cryopreserved in 20 cases because of the woman's age or premature ovarian failure. In 31 patients, ovarian tissue was frozen by a slow cooling technique using DMSO and sucrose as cryoprotectants. The patients were aged 2.7-34 years and 16 of them were <18 years old. Cryopreservation could be performed in all cases. Ovarian cortex histology was performed for all patients to evaluate the concentration of follicles. The mean number of primordial and primary follicles per mm(2) was 20.36 +/- 19.03 before 10 years of age, 4.13 +/- 2.9 between 10 and 15 years of age and 1.63 +/- 3.35 after 15 years of age. An average mean number of 26 +/- 8.2 ovarian fragments (range 13-50) were cryopreserved per patient for future autografts or for in-vitro growth of follicles.

CONCLUSION

Cryopreservation of ovarian tissue may be systematically proposed to young women and girls at risk of becoming sterile as a result of gonadotoxic treatment.

Cryopreservation of mouse embryos at morula/compact stage

PURPOSE

The objective of this article was to study mouse morula/compact stage embryo postthaw survival rates and postthaw developmental potential.

METHODS

Mouse morula/compact stage embryos were classified into 3 substages. Their morphological behavior during the freezing and thawing process were examined. Postthaw survival rates and blastocyst formation rates were compared between the three substages and the pronucleate and the 2-cell stage embryos. Finally, Postthaw fully compacted and late compact embryos were transferred to foster mothers.

RESULTS

Blastomeres of early compacting embryos separated from each other during the freezing process, whereas in fully compacted and late compact stages, the blastomeres remain compacted. Fully compacted and late compact stage embryos had higher Postthaw survival rates than other stages, though those were not statistically significant (P > 0.05). These two substages had significantly higher blastocyst formation rates than Postthaw pronucleate and early compacting embryos (P < 0.01). A total of 72 Postthaw fully compacted and late compact embryos were transferred and 20 live offspring were delivered.

CONCLUSIONS

After passing early compacting stage, fully compacted and late compact stage mouse embryos have high Postthaw survival rates and significantly higher blastocyst formation rates. Successful cryopreservation of embryos at these two substages has a significant value in embryo selection. The results obtained in this study may provide useful information for human assisted reproductive technology.

Frozen pronuclear oocytes: advantages for the patient

Since the first reported pregnancy in a human being after a frozen/thawed eight cell stage preembryo, cryopreservation of preembryos has been integrated as an important element of assisted reproductive technologies (ART). The cryopreservation technique has brought several advantages to ART. It allows the transfer of a limited number of embryos in the collection cycle, thereby reducing the risk of multiple pregnancies, and the patients have a reservoir of excess embryos for additional transfers. This maximises the number of embryo transfers per oocyte retrieval, while at the same time increasing the cumulative pregnancy rate from a given treatment cycle. Also, the ability to freeze all the embryos obtained and transfer at a subsequent cycle is useful in the avoidance of hyperstimulation syndrome, or when factors that may jeopardize implantation are apparent. Freezing of oocytes in a pronuclear stage has a valuable role in the management of infertility. Supernumerary zygotes can be cryopreserved safely for future transfer, avoiding additional inconvenience for the patients. The freezing thawing technique does not have any adverse effects on oocytes fertilized microsurgically. Pronuclear stage oocytes eventually survive the cryopreservation procedure better, yielding after culture cleaved embryos appropriate for transfer, which could increase the implantation rate. We believe that the cryopreservation of cleaved embryos, which is problematic, can be safely replaced by this procedure. This is not only an advantage for society as a whole, but also for the people involved in the process, as there should be no ethical or moral conflict for the patients or for the laboratory staff about discarding this material.

Children conceived by in vitro fertilisation after fresh embryo transfer

AIMS

To compare the outcome in in vitro fertilisation (IVF) children (after fresh embryo transfer) from multiple and singleton births with one another, and with normally conceived control children.

METHODS

A cohort of 278 children (150 singletons, 100 twins, 24 triplets and four quadruplets), conceived by IVF after three fresh embryos had been transferred, born between October 1984 and December 1991, and 278 normally conceived control children (all singletons), were followed up for four years after birth. They were assessed for neonatal conditions, minor congenital anomalies, major congenital malformations, cerebral palsy and other disabilities. Control children, all born at term, were matched for age, sex and social class.

RESULTS

The ratio of male:female births was 1.03. Forty six per cent of IVF children were from multiple births; 34.9% were from preterm deliveries; and 43.2% weighed less than 2500 g at birth. The IVF singletons were on average born one week earlier than the controls, weighed 400 g less, and had a threefold greater chance of being born by caesarean section. The higher percentage of preterm deliveries was largely due to multiple births and they contributed to neonatal conditions in 45.0% of all IVF children. The types of congenital abnormalities varied: 3.6% of IVF children and 2.5% of controls had minor congenital anomalies, and 2.5% of IVF children and none of the controls had major congenital malformations. The numbers of each specific type of congenital abnormality were small and were not significantly related to multiple births. IVF children (2.1%) and 0.4% of the controls had mild/moderate disabilities. They were all from multiple births, including two children with cerebral palsy who were triplets.

CONCLUSIONS

The outcome of IVF treatment leading to multiple births is less satisfactory than that in singletons because of neonatal conditions associated with preterm delivery and disabilities in later childhood. A reduction of multiple pregnancies by limiting the transfer of embryos to two instead of three remains a high priority.

Outcome in children from cryopreserved embryos

A cohort of 91 children from cryopreserved embryos and 83 control children who were conceived normally had their development assessed using the Griffiths's scales of mental development. The controls (81 singletons and two twins) of a similar age, sex, and social class were selected from siblings, cousins, and peers of the cryopreserved embryo group (68 singleton, 20 twins, and three triplets). Children from cryopreserved embryos had a lower mean birth weight and mean gestational age and a higher proportion were born by caesarean section. One child from the cryopreserved embryo group had Down's syndrome, three had squints, and four had conductive hearing loss while in the control children, six had squints, and nine had conductive hearing loss. In both groups, including the child with Down's syndrome, the mean Griffiths's quotient was greater than the standard 100. In the children from cryopreserved embryos, the singleton and multiple birth subgroups had statistically similar assessment results. The mean (SD) Griffiths's quotient was 105.69 (13.55) in children from cryopreserved embryos and 108.18 (9.80) in controls at a chronological age of 25.08 (12.86) and 29.19 (14.65) months respectively. Overall, the development in children from cryopreserved embryos did not cause concern though formal testing had highlighted small differences compared with other children conceived normally and of a similar social class.

Use of human zonae from cryopreserved oocytes in a test to assess the binding capacity of human spermatozoa

Aged unfertilized oocytes from an assisted conception programme were cryopreserved and then utilized after thawing in a zona-binding assay. Oocytes frozen using dimethyl sulphoxide (DMSO) showed poor survival post-thaw (2/40, 5%) compared to those frozen with propanediol (PROH) (63/134, 47%). When the zonae were exposed to spermatozoa from fertile donors, those frozen with DMSO showed a significantly higher number of bound spermatozoa than did those frozen with PROH (P < 0.002). In both groups, oocytes which failed to survive the freeze-thaw processes had greater numbers of bound spermatozoa than did those which survived (P < 0.05). Oocytes from cases of failed fertilization showed no difference in their rate of sperm binding compared with oocytes from cases in which some fertilization had occurred. Zonae frozen in PROH but which were from oocytes which were not viable after thawing were used to assess the binding of spermatozoa from men who had failed previously to fertilize their partner's oocytes in vitro and spermatozoa from men with poor quality semen and who had elected for treatment by micro-injection sperm transfer. The number of spermatozoa bound to zonae was reduced significantly in both groups compared to a fertile donor.

Assisted conception using buserelin and human menopausal gonadotrophins in women with polycystic ovary syndrome

OBJECTIVE

To compare the outcome of in vitro fertilisation (IVF) and gamete intrafallopian transfer (GIFT) cycles in women with or without ultrasound features of polycystic ovary syndrome (PCOS).

DESIGN

A consecutive series from January to December 1989.

SUBJECTS

Twenty-five women with PCOS scheduled for assisted conception. The controls were 139 women with normal ovaries.

SETTING

A single centre specialist fertility unit, Manchester, UK.

INTERVENTIONS

Pituitary desensitisation was with buserelin. In the PCOS group ovarian stimulation was with 1 ampoule (75 iu FSH) of hMG/day in 12 women (Group I) and two ampoules/day in 13 (Group II). The controls (Group III) were given two ampoules of hMG daily. Human chorionic gonadotrophin (hCG; 10,000 iu) was given when three follicles measured > or = 20 mm diameter.

MAIN OUTCOME MEASURES

Serum oestradiol (E2) concentrations, number of follicles, clinical pregnancies, features of the ovarian hyperstimulation syndrome (OHS).

RESULTS

Women with PCOS (Groups I or II) had more follicles > or = 14 mm diameter on the day of the hCG injection (P < 0.005), higher serum E2 concentrations on the day after the hCG (P < 0.05) and more oocytes retrieved (P < 0.05) than the controls. The OHS was more prevalent in those with PCOS (32% versus 6.5%; P < 0.05). The clinical pregnancy rate per embryo transfer (27% versus 22%) or gamete transfer (25% versus 39%) and the rate of spontaneous miscarriage (33% versus 12%) were not statistically different.

CONCLUSIONS

The pregnancy rate and outcome of pregnancy following IVF or GIFT in women with or without PCOS are similar. Women with PCOS are at a higher risk of developing OHS.

Does elective cryopreservation of all embryos from women at risk of ovarian hyperstimulation syndrome reduce the incidence of the condition?

OBJECTIVES

To analyse the incidence and factors associated with the ovarian hyperstimulation syndrome (OHS) in our IVF/GIFT programme before and after the introduction of a strategy to cryopreserve all embryos from women judged to be at risk.

DESIGN

Two hundred forty-one consecutive IVF/GIFT cycles from January to December 1989.

SETTING

Specialist fertility unit, Manchester, UK.

INTERVENTIONS

Pituitary suppression was effected by a daily subcutaneous injection of buserelin (500 micrograms) beginning 7 days before the expected menses. The ovarian stimulation was with variable amounts of human menopausal gonadotrophin. Ovulation was induced with 10,000 i.u. human chorionic gonadotrophin (hCG). From January to May (period A), gametes/embryos were replaced and 2000 i.u. hCG given, irrespective of the serum oestradiol (E2) concentration. From June to December (period B), all the embryos from women with an E2 > 3500 pg/ml on the day of ovulatory trigger were electively cryopreserved.

MAIN OUTCOME MEASURES

Serum E2, features of moderate or severe OHS, clinical pregnancies.

RESULTS

The OHS occurred in 10/105 (9.5%) and 12/136 (8.8%) cycles in periods A and B, respectively. Fewer women (6% versus 60%, P < 0.05) who had their embryos cryopreserved developed severe OHS compared with women with an E2 > 3500 pg/ml who became pregnant after gamete/embryo transfer in period A. The main factors associated with the development of OHS were serum E2 concentrations > 3500 pg/ml, whether gamete/embryos were replaced and the additional hCG given, the occurrence of a pregnancy and the presence of polycystic ovary disease.

CONCLUSION

The elective cryopreservation of all embryos from women with high E2 levels reduced the severity, but not the incidence of symptomatic OHS.