Pronuclear Scoring Research Articles

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

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. 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. 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%). 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.

Morphological scoring of human pronuclear zygotes for prediction of pregnancy outcome

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. 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. 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. 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.

High magnitude of light retardation by the zona pellucida is associated with conception cycles

Failures in expression of zona proteins correlate to subfertility in animals. Low expression of the zona proteins by the growing human oocyte may indicate reduced developmental potential. Therefore, we non-invasively analysed the thickness and the structure of the zona pellucida (ZP) of human oocytes with respect to embryo fate after ICSI. Retardance magnitude and thickness of the inner, middle and outer layers of the ZP were quantitatively analysed by a Polscope in 166 oocytes selected for transfer after ICSI (63 patients; 32.8 +/- 4.4 years) on the basis of pronuclear score at day 1. Blastomere number was determined at day 2. Data were compared between conception cycles (CC; 65 oocytes/23 patients) and non-conception cycles (NCC; 101 oocytes/40 patients) and with respect to maternal age. The thickness was slightly elevated (P < 0.001), and the mean magnitude of light retardance was nearly 30% higher (P < 0.001) in the inner layer of the zona pellucida of oocytes contributing to CC compared to NCC. Embryos in the CC group tended to develop faster. The magnitude of light retardance by the zona pellucida inner layer appears to present a unique non-invasive marker for oocyte developmental potential.

Examination of pronuclear patterns in a cohort of embryos selected for transfer on the basis of day 3 embryo score

Examination of pronuclear patterns in a cohort of embryos selected for transfer on the basis of day 3 embryo score

Elective single blastocyst transfer

Objective: Limiting the transfer to two blastocysts has become widely accepted in IVF practice as a successful modality to maintain high pregnancy rates while avoiding high order multiple births. The ideal scenario of a single embryo transfer has been primarily addressed in a few studies on young patients receiving a single cleavage stage embryo, selected by pronuclear scoring, early cleavage and day 2 and day 3 morphology. Success rates with single blastocyst transfer are based on theoretical estimates calculated from the implantation rates in studies where two blastocysts were transferred. The purpose of this study is to report our experience with elective single blastocyst transfer in patients up to the age of 40.

Pronuclear Scoring: correlation with Chromosome Complement

Pronuclear Scoring: correlation with Chromosome Complement

Pronuclear scoring as a predictor of embryo development

Many strategies have been proposed for the selection of viable embryos for transfer in human assisted reproduction. These have included morphological scoring criteria for day 1, 2, 3 and 5 embryos or combinations of these. Other strategies have used predictors such as timing of certain key events, as with early cleavage to the 2-cell, development to the 8-cell stage or patterns of fragmentation. All have shown some correlations with implantation. However, the overall success of these methods is still limited, with over 50% of all transferred embryos failing to implant. The use of pronuclear oocyte morphology has shown correlations with implantation and development to the blastocyst stage. The key aspects of pronuclear scoring, namely the presence of a cytoplasmic halo, the orientation of the nuclei in relation to the polar bodies and the size, number and pattern of distribution of nucleolar precursor bodies (NPB) in the nuclei were related to day 2,3 and 5 development, rate of development and day 3 and 5 morphology in a retrospective study. The pattern of the NPB or Z-score and the presence/absence of a halo had a significant effect on the rate of development on day 3 and day 5 and on the overall embryo morphology score. Low Z-score resulted in slow development, poor blastocyst formation and low morphology scores. The absence of a halo also resulted in slow and poor development, poor morphology, increased fragmentation and increased numbers of poor Z-scored embryos. The use of PN scoring can help predict embryos that have poor developmental potential, aid in early selection and may indicate the health of the oocyte.

Human pronuclear morphology is independent of maternal age and day 3 FSH in assisted reproductive technology (ART).

Objective: The morphology of human pronuclear embryos has been positively correlated to blastocyst development and implantation and therefore may be useful in achieving high clinical pregnancy rates while limiting the risk of high-order multiple gestations. Pronuclear scores have been shown to be both independent of maternal age and infertility diagnosis, further enhancing their prognostic value. The purpose of this study was to further define the predictive independence of pronuclear scoring by determining its relationship with maternal age and day 3 FSH.Design: Retrospective study of 326 consecutive ART cycles in a university-affiliated ART program.Materials/Methods: All patients undergoing ART from January to December 2000 were considered for analysis. Pronuclear scoring, maternal age, and serum day 3 FSH data were available for 282 cycles. Day 3 FSH results were obtained within one year of the start of the ART cycle. Patients with values ≥12 IU/L or age ≥43 years were excluded. Pronuclear scoring was performed the day following oocyte retrieval and insemination. Pronuclear embryos were scored as Z1, Z2, Z3, or Z4 based on nuclear size and alignment, and number and distribution of nucleoli as previously described (Scott et al., 2000). Distribution of high-grade pronuclear embryos (Z1 and Z2) was then compared with maternal age and day 3 FSH. Statistical evaluation was performed by regression analysis.Results: A total of 2548 pronuclear embryos were scored as Z1 (n = 893), Z2 (n = 854), Z3 (n = 542), or Z4 (n = 259). A scatter plot of the percentage of Z1 and Z2 pronuclear embryos versus maternal age demonstrated no apparent correlation. Similar results were obtained when high-grade pronuclear embryos were compared with day 3 FSH values. Regression analysis confirmed the lack of correlation of Z1 and Z2 pronuclear embryos with maternal age (R2 = 0.009) and day 3 FSH (R2 < 0.001).Conclusions: When performed in a group of patients undergoing ART, pronuclear scoring did not correlate with either maternal age or day 3 FSH serum levels. This observation indirectly supports the conclusion that pronuclear scoring may be a useful tool to predict outcome at ART, since the Z-score was independent of two variables that strongly influence ART outcome. Objective: The morphology of human pronuclear embryos has been positively correlated to blastocyst development and implantation and therefore may be useful in achieving high clinical pregnancy rates while limiting the risk of high-order multiple gestations. Pronuclear scores have been shown to be both independent of maternal age and infertility diagnosis, further enhancing their prognostic value. The purpose of this study was to further define the predictive independence of pronuclear scoring by determining its relationship with maternal age and day 3 FSH. Design: Retrospective study of 326 consecutive ART cycles in a university-affiliated ART program. Materials/Methods: All patients undergoing ART from January to December 2000 were considered for analysis. Pronuclear scoring, maternal age, and serum day 3 FSH data were available for 282 cycles. Day 3 FSH results were obtained within one year of the start of the ART cycle. Patients with values ≥12 IU/L or age ≥43 years were excluded. Pronuclear scoring was performed the day following oocyte retrieval and insemination. Pronuclear embryos were scored as Z1, Z2, Z3, or Z4 based on nuclear size and alignment, and number and distribution of nucleoli as previously described (Scott et al., 2000). Distribution of high-grade pronuclear embryos (Z1 and Z2) was then compared with maternal age and day 3 FSH. Statistical evaluation was performed by regression analysis. Results: A total of 2548 pronuclear embryos were scored as Z1 (n = 893), Z2 (n = 854), Z3 (n = 542), or Z4 (n = 259). A scatter plot of the percentage of Z1 and Z2 pronuclear embryos versus maternal age demonstrated no apparent correlation. Similar results were obtained when high-grade pronuclear embryos were compared with day 3 FSH values. Regression analysis confirmed the lack of correlation of Z1 and Z2 pronuclear embryos with maternal age (R2 = 0.009) and day 3 FSH (R2 < 0.001). Conclusions: When performed in a group of patients undergoing ART, pronuclear scoring did not correlate with either maternal age or day 3 FSH serum levels. This observation indirectly supports the conclusion that pronuclear scoring may be a useful tool to predict outcome at ART, since the Z-score was independent of two variables that strongly influence ART outcome.

Clinical use of a pronuclear stage scoring system following conventional in-vitro fertilization.

Objective: Human IVF has been developed for more than two decades. However, the relative low success rate may indicate that the criterion of selecting embryos, which was mainly based on the morphology and cleavage rate in routine clinic, was not enough. Pronuclear stage scoring was recently been used in IVF as an additional parameter. In this prospective study, modified pronuclear scoring system was used to score zygotes following conventional IVF. Design: Prospective evaluation of IVF results. Materials/Methods: This prospective analysis included 178 couples treated for infertility problems and following conventional IVF between July and December 2000. Couples underwent more than two cycles were excluded from this study. Pronuclear scoring was performed mainly based on the published system of Scott and Smith. The alignments of nucleoli at the junction of the two pronuclei, the position of the pronuclei, and the appearance of the cytoplasm were evaluated. To emphasize the importance of the synchrony between the two pronuclei, the nucleoli of polarized form of pattern 0 in the system of Tesarik and Greco was scored 5, and that of the non-polarized form of pattern 0 was scored 5′. Nucleoli beginning to align was scored 4. Scattered with big difference (3) was scored 3. If the pronuclei were well separated or were very unequal in size, they were scored 1. Close or aligned pronuclei were scored 5. Heterogeneous cytoplasm with a clear halo around the edges was scored 5, while pitted and/or darkened cytoplasm was scored 3. Pronclear membrane breakdown and early cleavage were not observed in this study. Results: A total of 178 treatment cycles were included in this study. Although pregnancy rate, implantation rate and multiple pregnancy rates increased with the increasing number of full score zygotes (pronuclear score = 15) in transferred embryos, however, no significant difference could be found. With mean pronuclear score (sum of all pronuclear oocytes selected/total number of pronuclear oocytes) was no less than 13, the pregnancy rate and implantation rate were 49.1% and 26.5% respectively, compared with 29.4% and 15.0% respectively when mean pronuclear score was less than 13. (P = 0.01 and P = 0.002 respectively). When all embryos were analyzed, 77.2% (1053 out of 1364) embryos developed from zygotes with pronuclear scores no less than 11 could be transferred or cryopresvered, while it decreased to 46.1% (88 out of 191) when pronuclear score was less than 11 (p < 0.001). Conclusions: In conclusion, pronuclear scoring is a very useful parameter, which may act as double-check to select embryos. A mean pronuclear score of 13 is a useful predictive value. However, pronuclear morphology could only partly represent embryo viability. Combination with the parameters of cleavage embryos to select transferred embryos is indispensable.

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.