Embryos with high implantation potential after intracytoplasmic sperm injection can be recognized by a simple, non-invasive examination of pronuclear morphology

Pregnancy outcome and live birth after IVF and ICSI according to embryo quality

PURPOSE

The pregnancy outcome and the chances of birth were assessed according to embryo quality after IVF or ICSI.

METHODS

The implantation rate (IR), the loss of gestational sacs rate (LGSR), and birth rate (BR) were determined according to the cleavage stage and the integrity of blastomeres after day-2 homogeneous embryo transfers (n = 1812).

RESULTS

The LGSR was higher after transfers of 2-3-cell or 5-6-cell embryos and was significantly increased when more than 20% of the embryo volume was fragmented in 4-cell embryos. After transfers of 4-cell embryos without fragmentation, the BR was significantly higher than the BR after transfers of 4-cell embryos with 1-20% fragmentation (16.6% vs 13.1%). The difference was the consequence of a higher IR (20.4% vs 17.3%) but also of a lower LGSR (18.9% vs 24.2%).

CONCLUSIONS

Not only implantation and the ability to give a pregnancy, but also the capacity to give a live birth are dependent on the embryo quality.

Developmental prognosis for zygotes based on pronuclear pattern: usefulness of pronuclear scoring

PURPOSE

To relate pronuclear patterns (PN) and zygote cytoplasmic appearance and embryo morphology.

METHODS

The usefulness of PN classification described by Tesarik et al. 1999 (patterns p0-5) and Scott et al. 2000 (Z1-4), for embryo selection is assessed.

RESULTS

Sinchrony on polarization and number of nucleolar precursor bodies (NPB) were associated with good quality embryos (p0 60.9% and p3 67.3%, and Z1 62.5% and Z2 64.7%; p<0.01). Pattern 4 zygotes were associated with small number of NPB developed into multinucleated embryos (14.3%) and poor quality embryos (61.9%). No significant differences were found in the pregnancy rate between transfer of at least one good prognosis PN pattern and transfer of poor prognosis PN patterns, although 75% of the transfers included at least one embryo derived from a pattern 0 zygote, and 55% included embryos from categories Z1 or Z2.

CONCLUSIONS

Sequential assessment involving the evaluation of oocyte quality, the classification of PN patterns and embryo morphology allows a more accurate evaluation of embryos to be selected for transfer.

Human blastocyst culture and derivation of embryonic stem cell lines

Human embryonic stem cell (hESC) biology is expected to revolutionize the future of medicine by the provision of cell-based therapies for the treatment of a variety of deliberatig diseases. The tremendous versatility of hESCs has reinforced this hope. To understand the biology of these mysterious cells and attempt to differentiate them into desirable tissues, bona fide hESCs that maintain their stability with time are required for research and clinical application. This review discusses the various protocols to derive and propagate hESCs from high quality embryos. The nature and properties of hESCs are also described together with unanswered questions that need to be addressed if this science is to be taken to the bedside.

Effect of embryo quality on pregnancy outcome following single embryo transfer in women with a diminished egg reserve

OBJECTIVE

To evaluate independently the effect of blastomere number and degree of fragmentation on pregnancy outcome following single ETs in women with a decreased egg reserve.

DESIGN

Retrospective cohort analysis.

SETTING

In vitro fertilization center of a university-based practice.

PATIENT(S)

Women having a single ET related to a decreased egg reserve. A requirement for inclusion was a day 3 serum FSH >12 mIU/mL and < or =3 antral follicles on ultrasound.

INTERVENTION(S)

Patients received no or minimal stimulation with gonadotropins.

MAIN OUTCOME MEASURE(S)

Pregnancy rates (PRs) following single ETs were evaluated according to blastomere number (group 1, < or =4 cells; group 2, 5 cells; group 3, 6 cells; group 4, 7 cells; and group 5, > or =8 cells) and fragmentation index (A, no fragmentation; B, 1-25% fragmentation; and C, >25% fragmentation). Embryo transfers and morphologic evaluation were performed on day 3.

RESULT(S)

The clinical and delivered PRs according to blastomere number showed that 6-8-cell embryos were six times more likely to implant than 4-5-cell embryos (6.6% versus 40.4% clinical). Degree of fragmentation did not predict outcome nearly as well as blastomere number. The overall clinical and delivered PRs per transfer were 27.8% and 24.1%, respectively, and were 14.8% and 12.8% per retrieval, respectively, and were 9.0% and 7.3% per initiated cycle, respectively.

CONCLUSION(S)

Six, seven, or eight-cell embryos have equal chances of implanting in women with day 3 elevated serum FSH. The key finding is that these embryos do better than those with <6 blastomeres. These data may be helpful in women with a diminished ovarian reserve in attempting IVF with their own eggs or when choosing donor oocytes.

Early cleavage: an additional predictor of high implantation rate following elective single embryo transfer

The value of early cleavage (EC) assessment is still being debated. The aim of this prospective study was to examine the predictive value of EC assessment performed exactly 26 h after insemination by IVF or intracytoplasmic sperm injection (ICSI) in a programme of elective single embryo transfer (SET) performed at day 2. If day 2 scoring demonstrated several embryos with high implantation potential, an EC embryo was transferred preferentially. EC was assessed only during normal laboratory hours so that there were two groups: EC assessed, and EC not assessed, the latter being the control. A total of 277 elective SET were performed in women under 37 years undergoing their first IVF or ICSI cycle (mean age 30.5 years, range 21-37). The overall clinical and ongoing pregnancy rates were 40.1% (111/277) and 32.9% (91/277) respectively. Significantly higher overall clinical and ongoing pregnancy rates were obtained after transfer of an EC embryo than a non-EC embryo: 49.4 versus 33.3% (P < 0.05) and 42.4 versus 25.9% (P < 0.02) respectively. However there was no significant difference between the EC assessed and control groups: 40.4 versus 39.3% and 33.2 versus 32.1 respectively. These findings confirm the value of EC assessment for selection of embryos with high implantation potential.

[How to improve assisted reproductive techniques results? Biological aspects]

In spite of recent improvements in IVF, pregnancy rates remained dramatically low. Better criteria are therefore necessary to establish the viability of a transferable top quality embryo. Observation of both pronuclei patterns at the zygote stage and early cleavage appears to offer an additional prognostic tool, correlating with chromosomal status and IVF outcome. Developmental ability and morphological evaluation of the embryo on days 2-3 remains the most used and valid method of selection, even though it is not sufficient to select embryos with the higher implantation potential. Blastocyst culture is another possible strategy for selecting the ideal embryo with theoretical, reduced risk of aneuploidies, though not all major chromosomal aberrations are excluded by prolonged in-vitro-culture. Concerning micro-manipulation of embryo such as hatching or cleaning or cytoplasm transfer, only controversial data are still available. In the field of ART, recent meta-analysis could not conclude to a positive effect concerning hatching, blastocyst culture or systematic PGD-AS (preimplantation genetic diagnosis with aneuploidy screening). Beside the technological aspect, Quality Management System is of great importance. Staff development and monitoring of staff performance in the IVF laboratory has to be considered in the next future.

Oocyte euploidy, pronuclear zygote morphology and embryo chromosomal complement

BACKGROUND

Pronuclear morphology has been proposed as an indicator of embryo development and chromosomal complement. In this study, the morphology of pronuclear zygotes generated from euploid oocytes [diagnosed by first polar body (PB1) analysis] was evaluated and compared with the configurations observed in chromosomally normal embryos (diagnosed by blastomere analysis).

MATERIALS AND METHODS

Group 1--238 patients underwent 273 assisted conception cycles in combination with the screening of aneuploidy on PB1 for the chromosomes 13, 15, 16, 18, 21 and 22. Only normal oocytes were inseminated. Group 2--218 patients underwent 318 assisted conception cycles with aneuploidy screening on day 3 embryos. In both groups, oocytes were checked for fertilization and pronuclear morphology at 16 h after insemination.

RESULTS

Seventy-three percent of zygotes from Group 1 had the configurations with centralized and juxtaposed pronuclei, large-size aligned or scattered nucleoli and PB located in the longitudinal or perpendicular axis of pronuclei. In Group 2, these configurations corresponded to those with the highest proportion of chromosomally normal embryos. Accordingly, in both groups, these configurations had a higher implantation rate than all the others.

CONCLUSIONS

These observations confirm that some patterns of pronuclear morphology are associated with a higher proportion of euploidy and implantation reaffirming the relevance of this scoring system for the prediction of zygote viability.

Beneficial effect of luteal-phase GnRH agonist administration on embryo implantation after ICSI in both GnRH agonist- and antagonist-treated ovarian stimulation cycles

BACKGROUND

GnRH agonist was recently suggested as a novel luteal-phase support that may act at different levels, including the pituitary gonadotrophs, the endometrium and the embryo itself. This prospective randomized study evaluates the effect of GnRH agonist administered in the luteal phase on ICSI outcomes in both GnRH agonist- and GnRH antagonist-treated ovarian stimulation protocols.

METHODS

Six hundred women about to undergo ovarian stimulation for ICSI (300 using a long GnRH agonist protocol and 300 using a GnRH antagonist protocol) were enrolled in this study. Patients treated with each of these two protocols were randomly assigned to receive a single injection of GnRH agonist or placebo 6 days after ICSI. Implantation and live birth rates were the primary outcomes.

RESULTS

Administration of 0.1 mg of GnRH agonist triptorelin on day 6 after ICSI led to a significant improvement of implantation and live birth rates after ICSI as compared with placebo. In GnRH antagonist-treated ovarian stimulation cycles, luteal-phase GnRH agonist also increased ongoing pregnancy rate. Moreover, luteal-phase GnRH agonist administration increased luteal-phase serum HCG, estradiol and progesterone concentrations in both ovarian stimulation regimens.

CONCLUSIONS

Luteal-phase GnRH agonist administration enhances ICSI clinical outcomes after GnRH agonist- and GnRH antagonist-treated ovarian stimulation cycles, possibly by a combination of effects on the embryo and the corpus luteum.

The limited importance of pronuclear scoring of human zygotes

BACKGROUND

Several studies have shown a correlation between the pronuclear morphology score (PNMS) and subsequent embryo development and implantation. Embryos with poor pronuclear score, elsewhere referred to as Z3 and Z4, are often not transferred or cryopreserved because it is believed that they have poor pregnancy potential. The objective of this study is to report our data on the use of the pronuclear score and its effect on pregnancy outcome.

METHODS

Retrospective analysis of IVF/ICSI-embryo transfer cycles completed over the course of 1 year (n = 334). Comparisons were made only in those groups of patients in whom cohorts of similarly scored PNMS embryos were transferred. The proportion of such homologous cohorts was 104/334 (31%). All other replacements were excluded from final analysis as they were dissimilar as far as PNMS is concerned. Pregnancy outcomes were evaluated.

RESULTS

The incidence of live birth resulting from the transfer of single pronuclear score homologous embryo types was 56 (14/25), 41 (13/32), 54 (23/43) and 0% (0/4) for PNMS scores 1, 2, 3 and 4, respectively. There was no correlation between PNMS category of the embryos transferred and live birth rates (P = 0.139).

CONCLUSIONS

PNMSs of 1, 2 or 3 do not correlate with live birth rates when assessing unique PNMS embryo transfers. In particular, previously considered poor (type 3) embryos can result in pregnancy with normal live birth rates. Whether type 4 embryos are compatible with normal development remains to be shown.

Limiting the number of injected oocytes to three impairs ICSI outcomes in patients with nonobstructive azoospermia

BACKGROUND

Since March 2004, only a maximum of three oocytes were allowed to be subjected to ICSI at one time in Italy. A previous study failed to show an impact of this restriction on fresh embryo transfer outcomes. The objective of this study was to compare ICSI outcomes before and after this restriction in patients with nonobstructive azoospermia.

METHODS

Patients underwent testicular sperm extraction followed by ICSI. Biological (fertilization rate and the percentage of good-morphology zygotes and embryos) and clinical (clinical pregnancy and implantation rates) outcomes of the last 100 ICSI attempts before the restriction and outcomes of the first 100 ICSI attempts after the restriction were compared.

RESULTS

Despite comparable fertilization rates (58.8% versus 59.2%; P > 0.05), there was a significant decrease in the percentage of good-morphology zygotes (41.1% versus 88.4%; P < 0.05) and embryos (36.7% versus 74.0%; P < 0.05) in the cohort of embryos transferred, clinical pregnancy rate (22.7% versus 42.4%; P < 0.05) and cumulative pregnancy rate from fresh and frozen embryo transfers (22.7% versus 53.5%; P < 0.05) after the restriction.

CONCLUSION

The oocyte number restriction reduces dramatically the chance of achieving a clinical pregnancy in cases of nonobstructive azoospermia.

IVF results: optimize not maximize

The desire to improve in vitro fertilization (IVF) results has led clinicians to replace more than 1 embryo in the uterus. As a result, multiple births have increased over the last 2 decades to epidemic proportions, exposing the field of assisted conception to justified criticism. This review aims to ensure that physicians involved in the field of fertility treatment are aware of the risks and complications related to multiple pregnancies, and to explore possible strategies such as blastocyst culture, preimplantation genetic screening, and embryo cryopreservation, which can help to control and reverse the tide of multiple pregnancies without reducing the good success rate that modern IVF treatment enjoys. A brief overview of the respective UK legislative system is also presented.

High-magnification ICSI overcomes paternal effect resistant to conventional ICSI

Previous studies have shown that repeated intracytoplasmic sperm injection (ICSI) failures can be caused by a paternal effect. Other studies have suggested that ICSI results are compromised if morphologically abnormal spermatozoa are injected into oocytes. This study was undertaken to evaluate the usefulness of a high-magnification optical system to select spermatozoa to be used for ICSI (high-magnification ICSI) in couples with repeated conventional ICSI failures. Couples with two or more previous conventional ICSI failures underwent an additional conventional ICSI attempt, followed by a high-magnification ICSI attempt. The outcomes of the two sequential attempts were compared. In 72 of these patients, sperm DNA integrity was assessed. In the whole group of 125 couples with repeated ICSI failures, high-magnification ICSI improved clinical outcomes (pregnancy, implantation, delivery and birth rates) without affecting biological outcomes (fertilization and cleavage rates, embryo morphology). The improvement of clinical ICSI outcomes was evident both in patients with an elevated degree of sperm DNA fragmentation and in those with normal sperm DNA status. It is concluded that high-magnification ICSI improves clinical outcomes in couples with previous repeated conventional ICSI failures.

Ultrastructural Dynamics of Human Reproduction, from Ovulation to Fertilization and Early Embryo Development1

This study describes the updated, fine structure of human gametes, the human fertilization process, and human embryos, mainly derived from assisted reproductive technology (ART). As clearly shown, the ultrastructure of human reproduction is a peculiar multistep process, which differs in part from that of other mammalian models, having some unique features. Particular attention has been devoted to the (1) sperm ultrastructure, likely "Tygerberg (Kruger) strict morphology criteria"; (2) mature oocyte, in which the MII spindle is barrel shaped, anastral, and lacking centrioles; (3) three-dimensional microarchitecture of the zona pellucida with its unique supramolecular filamentous organization; (4) sperm-egg interactions with the peculiarity of the sperm centrosome that activates the egg and organizes the sperm aster and mitotic spindles of the embryo; and (5) presence of viable cumulus cells whose metabolic activity is closely related to egg and embryo behavior in in vitro as well as in vivo conditions, in a sort of extraovarian "microfollicular unit." Even if the ultrastructural morphodynamic features of human fertilization are well understood, our knowledge about in vivo fertilization is still very limited and the complex sequence of in vivo biological steps involved in human reproduction is only partially reproduced in current ART procedures.

The value of pronuclear scoring for the success of IVF and ICSI-cycles

BACKGROUND

Pronuclear scoring helps to identify good quality embryos already at the pronuclear stage. There are no data available, however, to demonstrate whether patients benefit from a higher pregnancy rate after pronuclear scoring.

METHODS

In a retrospective, matched cohort study 338 cycles in which patients chose to score their oocytes at the pronuclear stage (scoring group) were compared with 338 cycles without scoring (control group). The cycles were matched for maternal age, number of previous IVF and ICSI cycles, cryopreservation (yes/no) and diagnosis of primary infertility.

RESULTS

The pregnancy rate was not significantly different between the scoring group and the control group (24.0 vs. 21.0%, NS) in spite of more cycles with grade A embryos and a higher number of embryos transferred. The presence of a Z1 pronuclear oocyte was found to be associated with the retrieval of more oocytes, a higher fertilization rate and more grade A embryos, as well as a non-significant increase in pregnancy rates (25.1 vs. 18.8%).

CONCLUSIONS

Benefit from pronuclear scoring seems to be small. Apparently, experienced biologists are able to select "good-quality" pronuclear oocytes in the same way they would do after scoring. However, the results might be biased by differences between the groups.

Relationship between pre-embryo pronuclear morphology (zygote score) and standard day 2 or 3 embryo morphology with regard to assisted reproductive technique outcomes

OBJECTIVE

To test the hypothesis that pregnancy rates are low if grade Z1 pre-embryos are not available for transfer and to determine if pronuclear morphology is a better predictor of pregnancy than traditional embryo morphology.

DESIGN

Prospective clinical study.

SETTING

Academic human reproduction laboratory.

PATIENT(S)

One hundred couples undergoing IVF with conventional insemination or ICSI.

INTERVENTION(S)

Embryo quality was assessed using both pre-embryo pronuclear morphology (zygote scoring or Z-scoring) at the time of fertilization evaluation and standard day 2 and day 3 embryo morphology (number of blastomeres and grading based on degree of fragmentation and blastomere size).

MAIN OUTCOME MEASURE(S)

We tested two decision models, one based on Z-scores and another on morphology, to determine which grading system better predicted pregnancy outcomes in assisted reproductive technique. Zygote score and embryo morphology were measured for all embryos and the transferred embryo pool. Implantation and pregnancy rates resulting from the embryo transfers of all cycles were calculated.

RESULT(S)

The Z-score distribution of 552 embryos was 27% Z1, 8% Z2, 50% Z3, and 15% Z4. Z1 and Z3 embryos had significantly (P approximately .03) higher quality over Z2 and Z4 embryos. Using the Z-score decision model with Z1 embryos having highest priority for transfer, pregnancy rates were similar between Z1 and Z3 embryos. Using embryo morphology as a decision model, pregnancy rates were highest in transfers containing one or two "best"-quality embryos.

CONCLUSION(S)

Z1 and Z3 embryos had similar morphology and pregnancy rates. The decision model based on the Z-score model was not better than standard embryo morphology in predicting pregnancy outcome.

Morphological scoring of human pronuclear zygotes for prediction of pregnancy outcome

BACKGROUND

As embryo selection is not allowed by law in Switzerland, we need a single early scoring system to identify zygotes with high implantation potential and to select zygotes for fresh transfer or cryopreservation. The underlying aim is to maximize the cumulated pregnancy rate while limiting the number of multiple pregnancies.

METHODS

In all, 613 fresh and 617 frozen-thawed zygotes were scored for proximity, orientation and centring of the pronuclei, cytoplasmic halo, and number and polarization of the nucleolar precursor bodies. From these individual scores, a cumulated pronuclear score (CPNS) was calculated. Correlation between CPNS and implantation was examined and compared between fresh and frozen-thawed zygotes. The effect of freezing on CPNS was also investigated.

RESULTS

CPNS was positively associated with embryo implantation in both fresh and frozen zygotes. With similar CPNS, frozen zygotes presented implantation rates as high as those of fresh zygotes. Nucleolar precursor bodies pattern and cytoplasmic halo appeared as the most important factors predictive of implantation for both types of zygotes, while pronuclei position was specifically relevant for frozen-thawed zygotes. Freezing induced an alteration of most zygote parameters, resulting in a significantly lower CPNS and a lower pregnancy rate.

CONCLUSIONS

CPNS may be used as a single prognostic tool for implantation of both fresh and frozen-thawed zygotes. Lower CPNS values of frozen-thawed zygotes may also be indicative of freezing damage to zygotes. Successful implantation of frozen zygotes despite lower CPNS suggests that they may recover after thawing and in vitro culture.

Significance of morphological attributes of the early embryo

There are many morphological transformations during development of human embryos that mainly involve phenomena that can be easily assessed in living embryos by simple non-invasive microscopical observation. A clear correlation between pronuclear morphology and the ability of the resulting embryo to continue developing and to implant has been described. There is also general agreement that a positive relationship exists between early embryo morphology and implantation rate. The parameters classically involved in embryo evaluation are: cleavage rate, blastomere symmetry, cytoplasmic appearance, extent of fragmentation and blastomere nuclear status. In this paper, morphological features that have been related to embryo developmental potential are described. Furthermore, the ability of a cumulative classification scheme developed in the laboratory to predict blastocyst formation and implantation is analysed.

ICSI in cases of sperm DNA damage: beneficial effect of oral antioxidant treatment

BACKGROUND

Most studies examining the use of ICSI for cases of elevated sperm DNA fragmentation report poor pregnancy and implantation rates. ICSI with testicular sperm samples has recently been suggested for these cases. Here we test a less invasive approach based on oral antioxidant treatment prior to ICSI with ejaculated spermatozoa.

METHODS

Thirty-eight men with an elevated (> or =15%) percentage of DNA-fragmented spermatozoa in the ejaculate were treated with antioxidants (1 g vitamin C and 1 g vitamin E daily) for 2 months after one failed ICSI attempt. In 29 (76%) of these cases this treatment led to a decrease in the percentage of DNA-fragmented spermatozoa, and a second ICSI attempt was performed. Outcomes of the two attempts were compared.

RESULTS

No differences in fertilization and cleavage rates or in embryo morphology were found between the ICSI attempts performed before and after the antioxidant treatment. However, a marked improvement of clinical pregnancy (48.2% versus 6.9%) and implantation (19.6% versus 2.2%) rates was observed after the antioxidant treatment as compared with the pretreatment ICSI outcomes.

CONCLUSIONS

Oral antioxidant treatment appears to improve ICSI outcomes in those patiens with sperm DNA damage, in whom this treatment reduces the percentage of damaged spermatozoa.

Improvement of delivery and live birth rates after ICSI in women aged >40 years by ovarian co-stimulation with growth hormone

BACKGROUND

Growth hormone (GH) is required for ovarian follicular development, and its administration during ovarian stimulation improves pregnancy rate in cow and sheep. Data on the use of exogenous GH in human assisted reproduction treatment are inconsistent. This prospective randomized study evaluates the usefulness of GH administration in women of >40 years undergoing ovarian stimulation for assisted reproduction treatment.

METHODS

One hundred women of >40 years undergoing assisted reproduction treatment were randomized between a GH treatment group and a placebo group. Assisted reproduction treatment outcomes were evaluated.

RESULTS

In patients of the GH treatment group, a similar number of oocytes, embryos and pregnancies was achieved as compared with the placebo group. However, the patients treated with GH suffered fewer pregnancy losses, resulting in higher delivery and live birth rates. These patients also showed higher peak serum estradiol concentration and higher concentrations of GH and estradiol in pre-ovulatory follicular fluid as compared with the placebo group.

CONCLUSIONS

Administration of GH during ovarian stimulation alleviates age-related decrease in assisted reproduction treatment efficiency. This effect appears to be mainly due to an improvement of oocyte developmental potential, but GH action on the uterus cannot be excluded.

Predicting embryo quality: mRNA expression and the preimplantation embryo

To overcome the low implantation rate (10-20%) following IVF in humans, more than two embryos are commonly replaced, potentially leading to high order multiple pregnancies with associated significantly elevated risks. Selecting the most viable embryos and transferring fewer of them could reduce this risk. Prolonged culture of embryos in vitro to the blastocyst stage may expose the embryo to hazards not normally encountered in the female reproductive tract. Recent studies comparing bovine oocyte maturation, fertilization and embryo culture in vivo and in vitro have demonstrated that the origin of the oocyte is the main factor affecting blastocyst yield, while the post-fertilization culture environment is crucial in determining blastocyst quality, measured in terms of cryotolerance and relative transcript abundance, irrespective of the origin of the oocyte. Production of embryos in vitro, particularly when using an extended period of in-vitro culture may predispose the embryo to phenomena such as 'large offspring syndrome', which is probably linked to altered gene expression, particularly of imprinted genes. Post-fertilization culture environment clearly has a profound effect on the relative abundance of gene transcripts within the embryo. Culture under sub-optimal conditions for even one day can lead to perturbations in the pattern of expression.

Paternal effects on cell division in the preimplantation embryo

Cell divisions in the human preimplantation embryo can be compromised by deficiencies in sperm nuclear genome or sperm-derived developmentally relevant cytoplasmic factors, oocyte activating substance and centriole. Sperm nuclear deficiencies are usually not detected before the 8-cell stage of embryo development, when a major expression of sperm-derived genes has begun. Sperm cytoplasmic deficiencies can be detected as early as the 1-cell zygote and then throughout the preimplantation development. The terms 'late paternal effect' and 'early paternal effect' have been suggested to denote these two pathological conditions. The late paternal effect is associated with an increased incidence of sperm DNA fragmentation. No association with sperm DNA damage has been found for the early paternal effect. The diagnosis of the late paternal effect is thus based on the examination of sperm DNA integrity, which should be performed in cases of repeated assisted reproduction failure even if morphologically normal embryos result from fertilization with the patient's spermatozoa. The only element leading to the diagnosis of the early paternal effect is poor zygote and embryo morphology and low cleavage speed. The absence of increased sperm DNA damage does not exclude the presence of this pathology. ICSI with testicular spermatozoa has recently been shown to be an efficient treatment for the late paternal effect. The use of oral antioxidant treatment in this indication has also given promising results.

Efficient treatment of infertility due to sperm DNA damage by ICSI with testicular spermatozoa

BACKGROUND

Sperm DNA damage (fragmentation) is a recently discovered cause of male infertility for which no efficient treatment has yet been found. Previous findings have suggested that clinically relevant sperm DNA damage may occur at the post-testicular level. This study was undertaken to assess the clinical usefulness of ICSI with testicular spermatozoa in this indication.

METHODS

The percentage of spermatozoa with fragmented DNA, assessed by terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labelling assay, and ICSI outcomes were compared in two sequential attempts performed, respectively, with ejaculated and testicular spermatozoa in 18 men with increased sperm DNA fragmentation.

RESULTS

The incidence of DNA fragmentation was markedly lower in testicular spermatozoa as compared with ejaculated spermatozoa. No differences in fertilization and cleavage rates and in embryo morphological grade were found between the ICSI attempts performed with ejaculated and with testicular spermatozoa. However, eight ongoing clinical pregnancies (four singleton and four twin) were achieved by ICSI with testicular spermatozoa (44.4% pregnancy rate; 20.7% implantation rate), whereas ICSI with ejaculated spermatozoa led to only one pregnancy which was spontaneously aborted.

CONCLUSIONS

These data show that ICSI with testicular spermatozoa provides the first efficient assisted reproduction treatment option for men with high levels of sperm DNA damage.

Selection of embryos for day-3 transfer at the pronuclear-stage and pronuclear-stage cryopreservation results in high delivery rates in fresh and frozen cycles

PURPOSE

Evaluate IVF-ET outcome data for a unique culture and cryopreservation strategy.

METHODS

Retrospective study of 92 patients. Embryos for day-3 transfer were selected at pronuclear-stage; all extra zygotes were cryopreserved at pronuclear-stage.

RESULTS

Delivery rates for Anonymous Oocyte Donation (Group I), patients <35 years (Group II), and 35-38 years (Group III) were 52.9%, 61.5%, and 51.7% for fresh and 38.5%, 33.3%, and 40.0% for frozen transfer. Deliveries per retrieval were 82.3%, 71.8%, and 58.6%. Only 0.88, 0.80, and 0.61 more zygotes were cultured than what were used for fresh transfer. Singleton, twin, and triplet rates were 64.6%, 31.2%, and 4.2% for fresh and 69.2%, 30.8%, and 0% for frozen.

CONCLUSIONS

Selection of day-3 transfer embryos at the pronuclear-stage and cryopreservation of extra zygotes results in high delivery rates in fresh and frozen cycles. This approach optimizes deliveries per retrieval and provides many patients with more than one pregnancy per retrieval.

Number of good quality embryos on day 3 is predictive for both pregnancy and implantation rates in in vitro fertilization/intracytoplasmic sperm injection cycles

OBJECTIVE

To evaluate the predictive value for implantation and pregnancy rates of the number of embryos that reach the eight-cell stage with less than 20% fragmentation (good quality embryos) on day 3.

DESIGN

Prospective observational study.

SETTING

Private IVF center.

PATIENT(S)

One hundred eighty-nine women undergoing IVF, or intracytoplasmic sperm injection with at least four zygotes, who have had three embryos transferred on day 3.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Pregnancy rate and implantation rate.

RESULT(S)

All patients (n = 189) had 3 embryos transferred. The patients were divided in five groups according to the number of good quality embryos on day 3 (0, 1, 2, 3, >3; respectively). For the five groups, the pregnancy rates were 2.9%, 33.3%, 45.5%, 39.4%, and 64.3%; the implantation rates were 2.0%, 17.0%, 20.5%, 19.3%, and 35.7%. No statistically significant differences in pregnancy rate or implantation rate were found for groups 1, 2, and 3 (when 1, 2, or 3 good quality embryos were present). The data were also analyzed after pooling these three groups. A statistically significant difference in pregnancy rate and implantation rate was found for group 0 (no good quality embryos), groups 1, 2, and 3 (1, 2, or 3 good quality embryos), and group >3 (>3 good quality embryos).

CONCLUSION(S)

The number of good quality embryos available on day 3 is a strong predictive value for both pregnancy rate and implantation rate. When good quality embryos are present on day 3, only two embryos should be transferred to minimize multiple pregnancies.

Single embryo transfer and IVF/ICSI outcome: a balanced appraisal

This review considers the value of single embryo transfer (SET) to prevent multiple pregnancies (MP) after IVF/ICSI. The incidence of MP (twins and higher order pregnancies) after IVF/ICSI is much higher (approximately 30%) than after natural conception (approximately 1%). Approximately half of all the neonates are multiples. The obstetric, neonatal and long-term consequences for the health of these children are enormous and costs incurred extremely high. Judicious SET is the only method to decrease this epidemic of iatrogenic multiple gestations. Clinical trials have shown that programmes with >50% of SET maintain high overall ongoing pregnancy rates ( approximately 30% per started cycle) while reducing the MP rate to <10%. Experience with SET remains largely European although the need to reduce MP is accepted worldwide. An important issue is how to select patients suitable for SET and embryos with a high putative implantation potential. The typical patient suitable for SET is young (aged <36 years) and in her first or second IVF/ICSI trial. Embryo selection is performed using one or a combination of embryo characteristics. Available evidence suggests that, for the overall population, day 3 and day 5 selection yield similar results but better than zygote selection results. Prospective studies correlating embryo characteristics with documented implantation potential, utilizing databases of individual embryos, are needed. The application of SET should be supported by other measures: reimbursement of IVF/ICSI (earned back by reducing costs), optimized cryopreservation to augment cumulative pregnancy rates per oocyte harvest and a standardized format for reporting results. To make SET the standard of care in the appropriate target group, there is a need for more clinical studies, for intensive counselling of patients, and for an increased sense of responsibility in patients, health care providers and health insurers.

A zygote is not an embryo: ethical and legal considerations

In spite of several past attempts at defining the point at which conception can be considered completed, resulting in the formation of an embryo, the existing definitions are still contradictory. In the absence of clear terminology, the application of laws aimed at the protection of early human life may have inadequate consequences for the efficacy of the current techniques of human infertility treatment. In this paper biological arguments are revisited, suggesting that the only point at which a clear demarcation line between what is and what is still not an embryo can be drawn is the moment of nuclear syngamy at the outset of the first cleavage division. The term 'zygote' is suggested to denote entities composed of spermatozoon and oocyte components before nuclear syngamy. It is suggested that the current embryo protection laws should not concern the zygote stage: at this stage, the main features that are said, in documents issued by different ethical and legal authorities, to characterize the early human embryo, namely the inseparable union of the male and female contribution, cell division and an autonomous control over cell division, are still not present. This reasoning strictly applies to embryos of biparental (paternal and maternal contribution) origin and cannot be extrapolated to embryos created by cell nuclear transfer (cloning). The application of embryo protection laws from the nuclear syngamy stage onwards can regulate embryo and embryo-derived stem cell research while still preserving the current high standard and efficacy of infertility treatment, which is of immediate interest to millions of infertile couples throughout the world.

[Prognostic factors of implantation]

One of the negative aspects of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) is the increased risk of multiple pregnancies. There is an epidemic of twin pregnancies with a higher risk of obstetric, perinatal and neonatal complications than singleton pregnancies and with an important psychosocial, economic and financial impact for the parents to be. A reduction in the number of twins can only be obtained by the transfer of one embryo. Single embryo transfer with an acceptable pregnancy rate might be considered if a top quality embryo is available. The need to characterize embryos with optimal implantation potential is obvious. A top quality embryo is characterized by the presence of 4 or 5 blastomeres at day 2 and at least 7 blastomeres on day 3 after insemination, the absence of multinucleated blastomeres and<20% cellular fragments on day 2 and day 3 after fertilization. Others prognostic factors of implantation are discussed in this review. Judicious application of eSET can halve the twinning rate while maintaining the overall pregnancy rate.

Pronuclear morphology predicts embryo development and chromosome constitution

The relationship between pronuclear morphology on the one hand, and embryo development and chromosomal status on the other, was evaluated in 68 couples scheduled to undergo preimplantation genetic diagnosis because of advanced maternal age or recurrent implantation failure. Zygotes were grouped according to their pronuclear (PN) morphology. During the period from fertilization to embryo transfer, cleavage rate, embryo quality, blastocyst formation and results of the chromosomal analysis of 240 embryos were recorded. Both embryo cleavage characteristics and chromosome constitution were related to PN morphology. Embryos developing from zygotes with the normal PN pattern (pattern 0) cleaved faster and formed embryos with better morphology as compared with zygotes with abnormal PN patterns. Aneuploidy rate of embryos derived from zygotes with the normal PN pattern, with a single PN anomaly and with a double PN anomaly was 25.6, 73 and 83% respectively. Chromosomally normal embryos with the normal PN pattern progressed to the blastocyst stage at a higher rate (90%) than chromosomally normal embryos with a single (61%) or a double (40%) PN anomaly. The same relationship applied to chromosomally abnormal embryos. It is concluded that PN morphology predicts both the risk of embryo developmental arrest and that of chromosomal abnormalities.

The graduated embryo score predicts the outcome of assisted reproductive technologies better than a single day 3 evaluation and achieves results associated with blastocyst transfer from day 3 embryo transfer

OBJECTIVE

To evaluate the graduated embryo score (GES) for predicting assisted reproductive technology (ART) outcome compared to a single morphologic evaluation on day 3 of culture (grade A: > or =7 cells; <20% fragmentation).

DESIGN

Prospective cohort analysis.

SETTING

Private practice.

PATIENT(S)

Women aged <40 years with a normal uterine cavity treated with ART (n = 106).

INTERVENTION(S)

Embryos were graded by GES and by day 3 morphologic characteristics alone before ET. Cycle outcomes were compared with embryo grade.

MAIN OUTCOME MEASURE(S)

Ongoing gestation and implantation rates.

RESULT(S)

Overall ongoing gestation and implantation rates were 48% and 26%, respectively. With 1+ embryo GES > or =70 (n = 77), the rates were 62% and 36%, respectively, which were significantly higher than for those with 0 embryos GES > or =70 (n = 29). With 1+ grade A embryo (n = 102), the rates were 50% and 27%, respectively. Transfer of more than one embryo GES > or =70 did not improve the pregnancy rate, but did increase the risk of multiple gestations. A single day 3 evaluation had an extremely low specificity (7%) compared to GES (47%). Graduated embryo scoring (GES) was an excellent predictor of pregnancy and implantation rates from blastocyst transfer. Day of transfer did not affect pregnancy rates, although implantation was higher from day 5 embryo transfer (ET) than from day 3 ET, as fewer embryos were transferred.

CONCLUSION(S)

Transfer of one or more embryo GES > or =70 predicts pregnancy and implantation rates better than a single morphologic evaluation on day 3 and achieves ART outcomes associated with blastocyst transfer from day 3 ET, making extended culture unnecessary for most patients.

Pronuclear morphology and chromosomal abnormalities as scoring criteria for embryo selection

OBJECTIVE

To verify whether a correlation exists between pronuclear zygote morphology and the chromosomal condition of preimplantation embryos.

DESIGN

Prospective analysis of pronuclear zygote morphology and preimplantation genetic diagnosis (PGD) for aneuploidy of the resulting embryos.

SETTING

Reproductive medicine unit, day surgery clinic.

PATIENT(S)

Seventy-seven patients undergoing 107 PGD cycles because of advanced maternal age (77 cycles) or previous IVF failures (30 cycles).

INTERVENTION(S)

Evaluation of pronuclear zygote morphology and chromosomal condition of the resulting embryos.

MAIN OUTCOME MEASURE(S)

Rate of embryo development, proportion of euploid embryos, and distribution of chromosomal abnormalities. The position of pronuclei within the ooplasm, the size and distribution of nucleoli, and the orientation of polar bodies with respect to pronuclei were highly predictive for the presence of complex chromosomal abnormalities in the developing embryos; zygotes with juxtaposed pronuclei, large-size nucleoli, and polar bodies with small angles subtended by pronuclei and polar bodies were the configurations associated with the highest rates of euploidy.

CONCLUSION(S)

The combination of the patterns related to pronuclear zygote morphology indicated four configurations where the proportion of chromosomally normal embryos was significantly higher compared with the other configurations, suggesting the validity of this scoring system for the selection of embryos generated by PGD patients.

Nucleolar precursor body distribution in pronuclei is correlated to chromosomal abnormalities in embryos

In-vitro generated human embryos have low implantation rates and high chromosomal abnormalities. Embryos are mostly selected on the basis of microscopic morphological examination. The relationship between pronuclear morphology and chromosomal abnormalities was investigated in this study. Zygotes were scored according to pronuclear morphology on day 1. Excess embryos that were not transferred or cryopreserved on day 3 were fixed. Chromosomes 13, 18, 21, X and Y were analysed by fluorescence in-situ hybridization (FISH). A total of 125 embryos were analysed; 58 (46%) were abnormal, 32 (26%) were mosaic and 35 (28%) were normal. Results were analysed according to different pronuclear morphology. Zygotes with polarized pattern had a significantly lower incidence of chromosome abnormality than those with a non-polarized pattern. The presence of cytoplasmic halo, the size of each pronucleus and the number of nucleolar precursor body had no significant effect on chromosomal abnormalities. In conclusion, embryos generated from zygotes with polarized pattern have fewer chromosomal abnormalities compared with other patterns. A simple microscopic examination during fertilization confirmation would be useful to select embryos with fewer chromosomal abnormalities, preferably in combination with other observations shown to correlate with chromosomal abnormalities.

Luteinizing hormone affects uterine receptivity independently of ovarian function

Previous studies have suggested that LH, in addition to its well-known effects on the ovary, may exert direct effects on the uterus. This study evaluated the effects of mid-cycle administration of human chorionic gonadotrophin (HCG), which signals through the LH receptor, on endometrial thickness and uterine receptivity in two groups of women lacking ovarian activity and receiving embryos from an oocyte donation programme. Patients in one group still had ovulatory cycles, but their ovarian function was suppressed by pituitary down-regulation with a gonadotrophin-releasing hormone (GnRH) agonist in the embryo transfer cycle, resulting in low endogenous LH concentrations. Patients in the other group were menopausal women whose pituitary function was not down-regulated in the embryo transfer cycle and whose endogenous LH concentrations were thus high. Patients in each of the two groups were randomized into two subgroups. Patients in one subgroup were given 5000 IU of HCG 2 days before oocyte recovery in the corresponding donor. Patients in the other subgroup received placebo at the same time. Oocytes from each donor were randomly distributed between one patient from the HCG subgroup and one patient from the placebo subgroup in each patient group. Endometrial growth and secretory transformation were stimulated by sequential treatment with oestradiol valerate and progesterone. In women with low endogenous LH receiving placebo, endometrial thickness stopped increasing at the beginning of secretory transformation. Mid-cycle HCG administration resulted in a continuous increase in endometrial thickness through this period, improved the implantation rate after embryo transfer in these women (30.6 versus 20.7%) and augmented the number of multiple pregnancies. No similar stagnation of endometrial thickness and no effects of mid-cycle HCG administration on endometrial thickness, the implantation rate and the number of multiple pregnancies were found in women with high endogenous LH. It is concluded that endometrial maturation is disturbed in women with low endogenous LH but can be rescued by mid-cycle stimulation of LH receptor with exogenous HCG in the absence of ovarian activity.

Does pronuclear morphology and/or early cleavage rate predict embryo implantation potential?

A total of 340 patients referred for in-vitro fertilization was included in a retrospective, comparative study in which zygotes were studied regarding alignment and polarization of nucleolar precursor bodies (NPB) and also early cleavage in relation to implantation and pregnancy rates for the 680 transferred embryos. At assessment of the pronucleus 18-19 h after sperm injection, NPB were checked for alignment/polarization. Twenty-six hours after sperm insemination the zygotes were assessed for early cleavage. At embryo transfer the two embryos with the best morphological score, irrespective of polarization and early cleavage, were selected for transfer. The overall rate of positive HCG tests 17 days after embryo transfer was 42% and the implantation rate 23%. Fourteen percent of the patients received two embryos with polarized NPB, with a positive HCG test of 51%. Embryo transfer with early-cleaved embryos was carried out in 21% of the cycles, with a pregnancy rate of 45%. Embryos with polarized NPB and/or early cleavage were transferred in 34% of the cycles, with a pregnancy rate of 51%, compared with a pregnancy rate of 38% when none of the embryos fulfilled these criteria (P-value 0.02). In this study the pregnancy rate was significantly higher when one or two embryos were polarized and/or early cleaved. It is concluded that in a cohort of morphologically good embryos, assessment for alignment/polarization of NPB and/or early cleavage can, together with conventional morphological criteria, serve as a simple non-invasive method for selection of embryos with high implantation potential.

Single embryo transfer – state of the art

Every practitioner active in the field of assisted reproduction treatment is aware of the risks and complications related to twin and higher-order multiple pregnancies. Introduction of single embryo transfer (SET) into IVF/intracytoplasmic sperm injection (ICSI) is one of the possible ways of reducing the rate of twin pregnancy. Careful selection of patients, in combination with elective SET, has been shown to decrease the twin pregnancy rate while maintaining a stable ongoing pregnancy rate. The combination of a woman younger than 38 years of age, in her first or second IVF/ICSI cycle and with an embryo with a high implantation potential is the key to successful SET. This article will discuss embryo selection and patient selection and review the data published on SET. In the Centre for Reproductive Medicine at Middelheim Hospital, 39% of all transfers in 2002 were SET; the ongoing pregnancy rate remained stable at 30.6%. The twin (multiple) pregnancy rate declined to 11.7%. Particular attention should be drawn to the augmenting effect of the pregnancy rate of frozen-thawed cycles. Health economic data available so far subscribe the plea for SET.

Pronuclear and morphological features as a cumulative score to select embryos in ICSI (intracytoplasmic sperm injection) cycles according to sperm origin

PURPOSE

To analyze best parameter to select embryos according to sperm origin in ICSI cycles.

METHODS

One hundred seventy-two ICSI cycles were divided among three different groups: A (ejaculated spermatozoa from nonmale factor infertility), B (ejaculated spermatozoa from oligospermia), and C (spermatozoa from azoospermia). Embryos were divided on Day 1 into two patterns: S0 (pronuclei (PN) aligned and close with normal arrangement of nucleoli) and S1 (when these characteristics were absent) and also on transfer day according to morphological features.

RESULTS

Relationships of PN patterns related to sperm origin were noted. More S0 embryos were detected with better sperm quality. Higher number of good quality embryos was obtained when male factor was absent. Ejaculated and epididymal spermatozoa provide better quality embryos than do testicular spermatozoa.

CONCLUSIONS

PN classification associated with transfer day morphology is valuable additional noninvasive criterion for elective embryo transfer, mainly in the cases with severe male factor.

Aspects of the molecular regulation of early mammalian development

Many regulatory systems operate in the early mammalian embryo. This brief overview surveys several systems and their integration including polarities and axes, left-right differentiation, timers in cells, tissues and in gene expression, and imprinting. Polarities are essential from the very earliest stages of oocyte formation, and maintain their significance until blastocyst stages and beyond. They determine cleavage axes and the distribution of maternal proteins in the oocyte, distinct distributions being identified at the animal pole especially. Left-right axes are no doubt expressed from the earliest embryonic stages, and perhaps even in determining slight differences in the axes of cleavage and of maternal protein distribution. Timers, equally fundamental, have been demonstrated to control many functions in oocytes and embryos. Many fundamental processes in early mammalian oocytes and embryos are closely timed. They are classified into circadian rhythms, hourglass timers, clocks regulating major aspects of development including transcription, longevity via telomere clocks and long-range systems. Imprinting and methylation, increasingly important in establishing stable phenotypes in early embryos, might develop abnormally under some circumstances including intracytoplasmic sperm injection and cloning. A general summary briefly describes some other aspects of regulation, especially chromosomal anomalies in human embryos.

Improvement in early human embryo development using new formulation sequential stage-specific culture media

OBJECTIVE

To determine whether altering selected components of sequential culture media can improve early development variables of human embryos.

DESIGN

Prospective, randomized, sibling oocyte split trial.

SETTING

Private ART center.

PATIENT(S)

Two hundred eight undergoing treatment with in vitro fertilization or microinjection.

INTERVENTION(S)

Oocytes from each patient were randomly allocated to fertilization and cleavage media of a control and a trial culture medium formulation.

MAIN OUTCOME MEASURE(S)

Rates of fertilization, cleavage, and uncontrolled division; average embryo morphology score; blastomeres per embryo; embryo score parameter (number of blastomeres x embryo morphology grade); and embryo utilization. The trial media resulted in a higher fertilization rate, higher cleavage rate, lower rate of uncontrolled division, higher number of blastomeres per embryo, higher average embryo morphology score, a higher embryo score parameter, and higher embryo utilization rate compared to the control media. All differences were statistically significant.

CONCLUSION(S)

Improved sequential stage-specific culture media can reduce the occurrence of severe human embryo fragmentation and improve developmental variables in early IVF- and ICSI-generated embryos.

Fundamentals of human embryonic growth in vitro and the selection of high-quality embryos for transfer

Knowledge of the nature of embryo growth, and the handling and scoring of quality in human embryos are significant aspects for embryologists in IVF clinics. This review describes the formation, growth and maturation of human oocytes, many aspects of fertilization in vitro, embryonic transcription during preimplantation stages, and the formation of polarities, timing controls, role of mitochondria and functions of endocrine and paracrine systems. Modern concepts are fully discussed, together with their significance in the practice of IVF. This knowledge is essential for the correct clinical care of human embryos growing in vitro, especially in view of their uncharacteristic tendency to vary widely in implantation potential. Underlying causes of such variation have not been identified. Stringent tests must be enforced to ensure human embryos develop under optimal conditions, and are scored for quality using the most advanced techniques. Optimal methods of culture are described, including methods such as co-culture introduced to improve embryo quality but less important today. Detailed attention is given to quality as assessed from embryonic characteristics determined by timers, polarities, disturbed embryo growth and anomalous cell cycles. Methods for classification are described. Approaches to single embryo transfers are described, including the use of sequential media to produce high-quality blastocysts. These approaches, and others involved in surgical methods to remove fragments, transfer ooplasm or utilize newer approaches such as preimplantation diagnosis of chromosomal complements in embryos are covered. New outlooks in this field are summarized.

Zygote versus embryo transfer: a prospective randomized multicenter trial

PURPOSE

To determine the efficiency of transferring human zygotes as opposed to human day 2 or 3 embryos.

METHODS

A prospective, randomized, Multicenter trial. Patients were randomized into zygote or embryo transfer. Patients were prepared for oocyte retrieval using standardized protocols. Oocyte retrieval was performed under general anesthesia. Oocytes and spermatozoa were treated using standard laboratory techniques. All protocols were coordinated by the coordinating center.

RESULTS

A total of 386 patients were included in the trial. Pregnancy rates were 36.5% after zygote transfer and 42% after embryo transfer. Implantation rates were equivalent (17%) in both groups.

CONCLUSIONS

No general difference was observed for zygote or embryo transfer. The results suggest that zygote transfer is a valid alternative to embryo transfer.

Day 3 embryo transfer with combined evaluation at the pronuclear and cleavage stages compares favourably with day 5 blastocyst transfer

BACKGROUND

The respective advantages of day 3 and day 5 embryo transfer are a matter of debate. Previous comparisons did not include pronuclear stage zygote scoring and cumulative success rates (fresh and cryopreserved embryos).

METHODS

Patients were randomized prospectively for day 3 or day 5 embryo transfer. Day 3 embryos were selected for transfer and cryopreservation by using combined evaluation at the pronuclear and cleavage stages.

RESULTS

There was no difference between day 3 and day 5 fresh embryo transfers as to the rates of pregnancy (58 versus 62%), clinical pregnancy (56 versus 58%), delivery (50 versus 48%), implantation (35 versus 38%) and birth (33 versus 36%) rates. The corresponding values for cryopreserved embryo transfers were also similar. However, day 3 embryo transfer compared favourably with day 5 transfer when the pregnancy (90 versus 66%), clinical pregnancy (85 versus 62%) and delivery (77 versus 52%) rates were calculated per oocyte recovery attempt.

CONCLUSIONS

With a selected population of good prognosis patients and our embryo selection criteria, the implantation potential of day 3 and day 5 embryos is equal. Per oocyte recovery attempt, day 3 transfer is more clinically efficient than day 5 transfer, but at least one transfer of cryopreserved embryos is necessary to manifest this superiority.

Factors controlling embryo viability

Many diverse factors affect embryo viability. The morphological measures routinely used to grade human embryos are of limited use as many of the factors influencing the longterm viability of embryos are genetic or molecular and are undetectable or inconclusive from visualization of living embryos by microscopy. This article presents examples of factors that are known to affect embryo viability, including gamete formation, embryonic genome activation, and im-printing. Aspects of both gamete and embryo development are addressed, and the possibility that various anomalies remain hidden for extended periods before impacting upon a later aspect of development is hypothesized. In future, more detailed and informative assessments of embryo viability before embryo transfer may require invasive approaches to study the composition of embryos at various stages of preimplantation development; however, indirect, non-invasive measures would be preferable.

Early cleavage of human embryos: an effective method for predicting successful IVF/ICSI outcome

BACKGROUND

The need for effective parameters for selecting the best embryos is paramount when a large number of them are available for transfer. Other studies have reported that transfer of pre-selected embryos, based on cleavage to the 2-cell stage at 25 h and 27 h post-insemination/intracytoplasmic sperm injection (ICSI), increases implantation and pregnancy rates. We investigated whether extending the time for selection of cleaved embryos to 29 h post-insemination/ICSI had a similar effect on pregnancy and implantation rates.

METHODS

Cleavage to the 2-cell stage was assessed at 25, 27 and 29 h post-insemination/ICSI. Embryos that had cleaved at any of these time points were designated as 'early cleavage' (EC), while others were designated as 'non-early cleavage' (NEC). EC embryos were selected and preferentially transferred.

RESULTS

EC occurred in 57% of the cycles (61% IVF; 51% ICSI). Significantly (P = 0.02) more clinical pregnancies occurred in the EC group (23/42, 55%) compared with the group that had no embryo undergoing first cleavage up to 29 h post-insemination/ICSI (8/32, 25%). The EC group of patients was significantly younger than the NEC.

CONCLUSION

Transfer of selected embryos that reached the 2-cell stage between 25 and 29 h post-insemination/ICSI is a reliable prognostic tool for patients undergoing assisted reproduction techniques.

Evaluation of pronuclear morphology as the only selection criterion for further embryo culture and transfer: results of a prospective multicentre study

BACKGROUND

The aim was to study zygote evaluation based on pronuclear morphology under the German embryo protection law, according to which only a maximum of three zygotes are allowed to be cultured for embryo transfer.

METHODS

In this prospective multicentre study, a total of 512 treatment cycles was performed at 10 centres, between November 1999 and October 2000. Zygotes were classified into seven patterns (0A, 0B and 1-5). Pattern 0A and 0B zygotes were preferentially used for further culture and transfer.

RESULTS

Cycles with transfer of at least one embryo derived from pattern 0B, but not pattern 0A, resulted in significantly higher pregnancy (37.9%) and implantation rates (20.5%) compared with non-pattern 0B cycles (26.4 and 15.7%; P < 0.05 and P < 0.01 respectively). In younger patients (aged < or =35 years), significantly more 0B zygotes were available for transfer than in older patients (34.2 versus 25.8%; P < 0.005).

CONCLUSIONS

From these data, it is concluded that evaluation of pronuclear morphology is beneficial, especially for countries with legal restrictions regarding embryo selection.

The predictive value of pronuclear morphology of zygotes in the assessment of human embryo quality

BACKGROUND

Recent studies have shown that zygote morphology could be used for the assessment of human embryo quality. Pronuclear (PN) morphology is based on certain distinct features seen in zygotes 16-18 h after fertilization. In the present study PN stage morphology was assessed and combined with a single embryo transfer in order to investigate whether currently used zygote classifications are able to predict embryo quality and implantation rates.

METHODS AND RESULTS

Zygotes were analysed according to two different classification systems. In the first, a total of 764 zygotes was analysed according to the degree of polarization of nucleolar precursor bodies (NPB). Zygotes with unpolarized PN (i.e. scattered localization of NPB) showed significantly slower (P < 0.005) cleavage rates (38.9%) than zygotes having at least one pronucleus polarized (57.3% and 54%). However, there was no difference in the pregnancy rate in 105 single embryo transfers between the groups. The appearance of a cytoplasmic halo was related to embryo morphology. Embryos derived from halo-positive zygotes had significantly better (P < 0.05) morphology (60.9%) compared to halo-negative derived embryos (52.2%), but in terms of pregnancy rates no difference was found. A total of 1520 zygotes was analysed according to a second classification system, which was based on the number and distribution of NPB. In the comparative analysis, none of the six different classes produced superior quality embryos or higher pregnancy rates in 144 single embryo transfers.

CONCLUSIONS

Our results indicate that there are no significant differences in embryo quality or implantation/pregnancy rates between proposed zygote classes.

The Graduated Embryo Score (GES) predicts blastocyst formation and pregnancy rate from cleavage-stage embryos

BACKGROUND

Embryo morphology and cleavage rates alone do not consistently identify embryos with high implantation potential following IVF. Blastocyst transfer has been reported to improve success rates by identifying potentially superior quality embryos. Algorithms for predicting IVF outcomes based on the presence of early developmental milestones have been proposed. Here we introduce the Graduated Embryo Score (GES).

METHODS

Nucleolar alignment along the pronuclear axis, regular cleavage and degree of fragmentation at the first cell division, and cell number and morphology on day 3 were weighted to create a possible GES of 100 for each of 1245 fertilized embryos derived from 109 patients aged <40 years. The GES was correlated with IVF outcome.

RESULTS

Of 983 embryos for extended culture, 349 (36%) developed to blastocyst and 180 (18%) were good quality (grade I-II). When ranked by cell number and morphology alone, 34% of embryos with > or =7 cells and <20% fragmentation formed good quality blastocysts. Using GES, embryos scoring 90-100 had 64% blastocyst formation compared with 31% scoring 70-85 and with 11% scoring 30-65. Embryos scoring 70-100 had 44% blastocyst development compared with 9% scoring 0-65. Fifty-six patients (51%) conceived on-going gestations from 294 transferred embryos. In patients with at least one transferred embryo scoring > or =70, the pregnancy rate was 59% compared with 34% if all embryos scored <70. The overall implantation rate was 28%. Among embryos scoring 70-100, an implantation rate of 39% was seen, compared with 24% among embryos scoring 0-65.

CONCLUSIONS

Predicting which cleaved embryos will form blastocysts could permit the high success rates associated with blastocyst transfer to be achieved from day 3 embryo transfer.

Zygote evaluation: an efficient tool for embryo selection

One of the main problems concerning IVF units is the need to decrease the occurrence of multiple pregnancies in their practice without affecting the overall success rate. Different embryological parameters concerning every step of the early embryo development are known to have some predictive value for implantation potential. In this prospective study, a pronuclear scoring system was used to classify zygotes into six patterns from 0 to 5. Cleaved, day 3 embryos developed from pattern 0 zygotes, which was described as the normal pattern, were transferred when available. For each zygote pattern, the subsequent embryological development was analysed. Pattern 0 zygotes led to significantly more 'good quality' embryos with higher implantation potential than embryos developing from the other zygote patterns (P < 0.01). Embryo transfers including at least one pattern 0 resulted in significantly more pregnancies than transfers without any pattern 0 zygotes (39.3 versus 19.7%, P < 0. 01). No relationship between clinical parameters (age of female partner, infertility cause) and zygote pattern distribution was demonstrated.