The relationship of pronuclear stage morphology and chromosome status at cleavage stage

Pre-implantation genetic screening among women experiencing recurrent failure of in vitro fertilization

OBJECTIVE

To determine the efficiency of pre-implantation genetic screening (PGS) among women scheduled to undergo intracytoplasmic sperm injection who had experienced recurrent in vitro fertilization (IVF) failure.

METHODS

The present retrospective cohort study reviewed the medical records of consecutive women who had experienced recurrent IVF failure and had presented at a private IVF facility in Trabzon Province, Turkey, to undergo intracytoplasmic sperm injection between May 1, 2012, and December 31, 2014. Patient data and perinatal outcomes were compared between patients who underwent PGS and those who did not.

RESULTS

There were 88 patients included in the study; 43 patients had undergone PGS and 45 had declined to do so. No differences were detected in the clinical pregnancy rate (P=0.846), spontaneous abortion rate (P=0.416), number of perinatal deaths (P=0.162), or the number of live deliveries (P=0.188) between the groups of patients. The pregnancies included in the study resulted in 25 neonates being delivered; 24 had normal karyotypes, and one neonate from the control group had a karyotype of 46, XX, 9ph. Among the 19 embryos that were not transferred, the most frequently encountered chromosomal anomalies were diploidy, monosomy X, and 2N/N/4N mosaicism, detected in 7 (37%), 2 (11%), and 2 (11%) embryos, respectively.

CONCLUSION

PGS had no effect on perinatal outcomes among women experiencing recurrent IVF failure.

Preimplantation genetic diagnosis by fluorescence in situ hybridization of reciprocal and Robertsonian translocations

OBJECTIVE

The presence of reciprocal and Robertsonian chromosomal rearrangement is often related to recurrent miscarriage. Using preimplantation genetic diagnosis, the abortion rate can be decreased. Cases treated at our center were reviewed.

MATERIALS AND METHODS

A retrospective analysis for either Robertsonian or reciprocal translocations was performed on all completed cycles of preimplantation genetic diagnosis at our center since the first reported case in 2004 until the end of 2010. Day 3 embryo biopsies were carried out, and the biopsied cell was checked by fluorescent in situ hybridization using relevant informative probes. Embryos with a normal or balanced translocation karyotype were transferred on Day 4.

RESULTS

Thirty-eight preimplantation genetic diagnosis cycles involving 17 couples were completed. A total of 450 (82.6%) of the total oocytes were MII oocytes, and 158 (60.0%) of the two-pronuclei embryos were biopsied. In 41.4% of the fluorescent in situ hybridization analyses, the results were either normal or balanced. Embryos were transferred back after 21 cycles. Three babies were born from Robertsonian translocation carriers and another two from reciprocal translocation carriers. The miscarriage rate was 0%. Among the reciprocal translocation group, the live delivery rate was 8.3% per ovum pick-up cycle and 18.2% per embryo transfer cycle. Among the Robertsonian translocation group, the live delivery rate was 14.3% per ovum pick-up cycle and 20.0% per embryo transfer cycle.

CONCLUSION

There is a trend whereby the outcome for Robertsonian translocation group carriers is better than that for reciprocal translocation group carriers. Aneuploidy screening may possibly be added in order to improve the outcome, especially for individuals with an advanced maternal age. The emergence of an array-based technology should help improve this type of analysis.

Embryo culture and selection: morphological criteria

In this chapter, we have outlined the various morphological criteria for selection of the best embryo at each important milestone encountered in the progress from the oocyte to the blastocyst. As Gerris et al. stated, a combination of one, two, or even three selection points should lead to a more accurate selection of the best embryo, as no one criterion is better than the other. An embryo that fails to meet the entire set of selection criteria must be avoided as culture cannot correct an impaired embryo.

Pronuclear morphology evaluation for fresh in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) cycles: a systematic review

The current systematic review was aimed to assess the effectiveness of the zygote morphology evaluation in fresh in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) cycles. All available studies reporting on zygote morphology and clinical and/or biological outcomes were analyzed. Forty studies were included in the final analysis. Fourteen different zygote scoring systems were employed. Zygote morphology correlated significantly with embryo quality and cleavage, blastocyst stage, embryonic chromosome status, in a high proportion of the studies which assessed the specific outcome [15/25 (60%), 15/20 (75%), 7/8 (87.5%), 6/6 (100%), respectively]. On the other hand, only a reduced proportion of papers showed a statistically significant relationship between implantation, pregnancy and delivery/live-birth rates and zygote morphology score [12/23 (52.2%), 12/25 (48%), 1/4 (25%), respectively]. In conclusion, our findings demonstrate the lack of conclusive data on the clinical efficacy of the zygote morphology evaluation in fresh IVF/ICSI cycles, even if biological results showing a good relationship with embryo viability suggest a role in cycles in which the transfer/freezing is performed at day 1.

Pronuclear morphology, embryo development and chromosome constitution

The aim of the present study was to evaluate the usefulness of pronuclear patterns, according to the classifications of Tesarik and Scott, as predictors of embryo chromosome constitution. Up to 73 preimplantation genetic diagnosis/preimplantation genetic screening (PGD/PGS) cycles were analysed in this retrospective study including 17 cycles of translocation carriers and 56 PGS cycles. A total of 331 biopsied embryos were studied assessing pronuclear (PN) pattern, embryo quality and chromosome constitution. As regards to the relationship between PN pattern and embryo quality, the data obtained in this study show no correlation between both parameters. Although there were no significant differences when comparing the distribution of chromosomally normal and abnormal embryos with respect to embryo quality, such differences were observed when distinguishing between normal, aneuploid and polyploid embryos. The results show that the PN pattern using Tesarik's and Scott's classification systems is not related to the embryo developmental potential or its chromosome constitution. Therefore, in the context of a PGD/PGS programme, the PN pattern cannot be used as a tool to predict embryo quality or chromosome status.

Relationship between pronuclear scoring and embryo quality and implantation potential in IVF-ET

To assess the relationship between pronuclear scoring and day-3 embryo quality and pregnancy outcome and to determine the clinical value of pronuclear stage scoring system in human in vitro fertilization-embryo transfer (IVF-ET) program, a pronuclear scoring system was used to score zygotes 16-20 h after insemination during conventional IVF or intracytoplasmic sperm injection (ICSI). The embryos were classified into groups Z1, Z2, Z3 and Z4. Comparisons were made of the rates of arrested embryos and excellent embryos on day 3. Comparisons of pregnancy outcome were made only in those patients in whom cohorts of similarly Z-scored embryos were transferred. The results showed that there were less arrested embryos and more excellent embryos on day 3 in groups Z1 and Z2 than those in group Z3 and Z4. More embryos arrested and less excellent embryos developed in group Z4 than group Z3. The clinical pregnancy rates resulting from the transfer of single pronuclear score homologous embryo types were similar among groups Z1, Z2 and Z3. Implantation rates of group Z1 were higher (P<0.05) than that of group Z3. These findings suggests that pronuclear scoring can predict developmental ability on day 3 and implantation potential. A evaluation that combines the Z-score and day 3 embryo morphology is useful in the determination of the most viable embryos and the number of embryos for transfer.

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.

Morphologic parameters of early cleavage-stage embryos that correlate with fetal development and delivery: prospective and applied data for increased pregnancy rates

BACKGROUND

Many different embryo selection criteria have been used in assisted reproductive technologies (ART), but there are no published prospective studies to ascertain their usefulness in predicting implantation.

METHODS

In a prospective trial, 20 early scoring parameters previously reported to influence clinical outcome were collected, but embryos were selected for transfer by current laboratory protocols; day 1 pronuclear (PN) (Z) score combined with day 3 or 5 morphology. Data points for each oocyte/embryo were scored independently and tracked individually. Data were analysed retrospectively for parameters most likely to result in a positive pregnancy test, fetal heartbeat (FHB) and delivery.

RESULTS

Results indicated that day 1 PN morphology and nucleolar precursor body (NPB) ratio, day 2 cell number, blastomere symmetry and nucleation and the ability to cleave from day 2 to day 3 were the six most significant factors in fetal development. This outcome was then applied prospectively over 8 months. The implantation rate (IR) and clinical pregnancy rate (CPR) increased in each age group, and the number of embryos used decreased.

CONCLUSION

In conclusion, early parameters that include PN morphology, number and ratio of NPBs per nucleus and the day 2 morphology of cleaving embryos are stronger positive predictors of implantation than day 3 morphology or the ability to achieve the blastocyst stage of development. Parameters that were most consistently correlated with no delivery were lack of PN symmetry, day 2 multinucleation and uneven cell size. Day 3 and day 5 parameters were not significant compared with the combination of early parameters.

Light retardance by human oocyte spindle is positively related to pronuclear score after ICSI

Disturbed spindle assembly increases risks of chromosome mal-segregation. Non-invasive polarization microscopy (PolScope) was employed in two centres to assess spindle integrity for the first time quantitatively in human oocytes from consenting patients undergoing intracytoplasmic sperm injection (ICSI) with respect to pronuclear (PN) score after fertilization. In one centre oocytes were selected before ICSI, in another selection was after ICSI according to PN score. In both centres, mean retardance of light by birefringent spindles in oocytes forming a pre-embryo with good PN score after ICSI was significantly higher compared with spindles in oocytes developing into a lower PN score pre-embryo with limited developmental potential (P < 0.001). Transfers involving oocytes with high retardance and at least one good PN score embryo resulted more frequently in a conception than transfers from oocytes with spindles of lower mean retardance and lower PN score embryos. There was a trend for an inverse relationship between age and magnitude of retardance in a small oocyte cohort. The study suggests that quantitative evaluation of mean retardance of light by the oocyte spindle predicts oocyte health, is related to PN score of the embryo and may be especially useful to assess oocyte quality in countries with legal restrictions to select after fertilization.

Association of pronuclear Z score with rates of aneuploidy in in vitro-fertilised embryos

The present study aimed to correlate the Z-scoring system to outcomes in in vitro fertilisation (IVF) cycles performed in conjunction with preimplantation genetic diagnosis. In 178 cycles, a total of 468 pronuclear embryos was scored prospectively using the Z score before culture and biopsy on Day 3 to detect chromosomes 13, 16, 18, 21, 22, X and Y. The results showed significant differences between Z1 and Z4 scoring embryos, with Z1 giving an increased biopsy rate (83.3% v. 51.1%), embryo quality (≥fair: 83.3% v. 57.8%) and embryo growth rate (≥six cells: 87.0% v. 44.4%). The incidence of chromosomally normal embryos decreased from Z1 to Z4 (Z1: 40%; Z2: 29.7%; Z3: 22.7%; Z4: 13.6%; P < 0.04). Thus, the Z scoring, mainly Z1 and Z4, correlated significantly with the expected embryo outcomes and preimplantation genetic diagnosis findings. Further improvement of pronuclear scoring with the use of a two-stage assessment is proposed.