Evaluating the Role of First Polar Body Morphology on Rates of Fertilization and Embryo Development in ICSI Cycles

One of the most important factors that determine success in assisted reproductive technology (ART) is the oocyte. It is clear that the quality of oocytes can affect fertilization and embryo development (1). By introduction of intracytoplasmic sperm injection (ICSI), many couples with male factor infertility have taken this opportunity to overcome their infertility. One of the capabilities of ICSI is the evaluation of oocyte morphology and maturity after denudation of cumulus cells for microinjection. The majority of all metaphase II (MII) oocytes (60%-70%) have at least one morphological abnormality (2). Many studies have reported the effect of morphological characteristics of oocytes on fertilization rate and embryo development. The outcome of ART is dependent on both patient parameters and embryo variables (3). Evaluation of first polar body (1^st PB) morphology is useful for distinguishing the post-ovulatory age of the oocyte (4). Correlation between oocyte morphology and ICSI outcome is still a matter of controversy (5-9).

Ebner et al. (10) have reported that the 1^st PB shape can affect fertilization rate and embryo quality in ICSI cycles. Recent studies have also demonstrated the relationship of 1^st PB morphology to mature oocyte viability, which may be used as a prognostic factor to predict oocyte performance and pregnancy achievement after an ICSI treatment (11, 12). Some studies have shown a correlation between oocyte performance and 1^st PB morphology during ICSI treatment cycles (9,10,13-15). However, others did not show any correlation between 1^st PB and ICSI outcomes (16-19).

Additionally, the correlation between blastocyst formation, implantation rate and 1^st PB morphology has been reported by Ebner and colleagues in 2002 (14). Germinal vesicle breakdown (GVBD) and simultaneous extrusion of the 1^st PB shows completion of the first meiotic division in human oocytes. As a result, the 1^st PB is a marker which indicates that the oocyte is ready to undergo the fertilization process. This event is synchronized with nuclear and cytoplasmic maturation (20) The main goal of this prospective study is to evaluate the correlation of 1^st PB morphological characteristics with rates of fertilization and embryo development in ICSI cycles.

A total of 286 oocytes were normally fertilized, of which 179 were normal and 107 had fragmented 1^st PBs. Additionally, 287 embryos were formed of which 179 were good embryos (119 normal oocytes and 60 fragmented 1^st PB). From the total of 287 embryos, 213 had early cleavage that resulted from 139 normal oocytes and 74 fragmented 1^st PB (Table 1).

The data showed that 27% of the oocytes had fragmented 1^st PB with no other morphological abnormalities, while the remainder were associated with other abnormalities. There were 46.1% of the oocytes that had double defects and 26.9% of the oocytes had multiple defects. In group B, RF (19%) and granulation (9%) were double defects; wPVS with RF (10%) were the most common abnormalities observed for multiple defects. Overall, other abnormalities with fragmentation of 1^st PB for both double and multiple defect oocytes was less than 10%. The least anomaly combined with 1^st PB fragmentation was darkness in the oocyte cytoplasm (0.6%). For oocytes with multiple defects, the least common anomaly was bull’s eye with debris in the PVS (0.6%).

There was no significant relationship between groups A and B in terms of oocyte fertilization rate; 1^st PB morphology did not predict fertilization rate. The rates of good embryo formation for groups A was 66.5%, whereas it was 55.6% for group B. Cleavage rates for group A was 77.7% and 68.5% for group B. The embryo development rates were not statistically significant in the two groups (Table 2).

Women with group A had a mean age of 32.3 ± 0.3 years, whereas those with group B were 32.8 ± 0.4 years, which was not statistically significant. However, we found a significant difference between maternal age in groups A and B (p=0.016) with regard to the formation of good embryos (Table 3).

Because of different nuclear maturity, the retrieved oocytes post ovarian hyper-stimulation show different grades of 1^st PB morphology. The presence of 1^st PB and its observation by an embryologist before ICSI is very important because extrusion of the 1^st PB reflects MII oocyte maturity. One of the attractive issues in ART is finding criteria(s) to predict which oocytes will fertilize and which oocyte characteristic(s) may affect embryo development during the ART procedure.

Our results demonstrate no correlation between 1^st PB morphology and fertilization rate, embryo quality or even cleavage rate in women undergoing ICSI treatments. There is no significant difference between maternal age in groups A and B. Also, patients’ ages were not related to fertilization and cleavage rates, similar to the findings of Ciotti et al. (16) but is related to embryo quality. In the literature, the prognostic value of 1^st PB morphology for fertilization rate, embryo quality and cleavage rate is controversial. Our findings are similar to previous studies reported by reproductive scientists (11, 14-17, 19, 24, 25), but conflict with reports from others (9, 10, 13). One reason for this contradiction may be related to the methodological variation in oocyte evaluation. Xia (9) and Mikkelsen and Collouge (24) have reported that the 1^st PB morphology combined with perivitelline space and cytoplasmic inclusions can be used as prognostic factors for fertilization rate and cleavaged embryo quality (9, 24), however we only evaluated 1^st PB morphology. The other reason for this discrepancy may be related to the use of a different 1^st PB grading system. Some studies divide 1^st PB morphology simply into two groups of normal and fragmented, as we did. However, others may grade 1^st PB according to criteria such as surface, size and maturity (9, 10, 13).

Considering the positive relationship between 1^st PB morphology and time elapsed in culture, therefore, PB morphology may alter after a few hours, and it can change according to the timing of the observation. Ciotti et al. have noted that 1^st PB fragmentation is related to the time elapse between retrieval, denudation and ICSI performance (16). They checked a subgroup of oocytes twice (at the moment of denudation and injection, respectively) for 1^st PB fragmentation and have observed different degrees of fragmentation at the first and second efforts (11.1% and 22.8%, respectively). However, as they increased the time elapsed for denudation to >3.5 hours, the fragmentation rate of the oocytes was 26.7%. Another dispensary may be related to the procedure that occurs for the time of the 1^st PB evaluation and performing the ICSI. In different studies, distinct ICSI procedures were applied, but timing for cumulus cell denudation and ultimately the time in which the 1^st PB was evaluated may not be the same. It is well known that, because of controlled ovarian hyperstimulation, not all retrieved oocytes have the same quality, and different ovarian hyperstimulation protocols may be applied in studies. Therefore, oocyte quality may be influenced by the aforementioned protocols.

Moreover, Verlinsky and his colleagues in 2003 have shown that PB morphology is not related to the genotype analyzed for aneuploidy in patients who underwent preimplantation genetic diagnosis (PGD). They noticed no correlation between polar body shape and genetic constitution of the oocyte (19). In addition, they detected 1^st PB morphology grading changes in terms of fragmentation in over one-third of the oocytes studied. Hence, 1^st PB morphology assessment may not serve as a reliable marker for assessment of oocyte quality and competence.

The data demonstrated that 1^st PB morphology does not appear to be a prognostic factor for oocyte competence in the process of fertilization and early embryo development in ICSI cycles.