One of the main items of IVF treatments is maintain an high performance in terms of pregnancy rate reducing at same time the multiple gestations; the selection of the best embryo/embryos to transfer is a key step to achieve this objective. Nowadays, the embryo selection is mainly performed on the basis of visible morphological parameters [2–5], but this assessment can not provide any information about embryonic aneuploidies, a problem increasing with the advancing maternal age [32, 33], and probably implicated in the most of the first-trimester spontaneous miscarriages . The evaluation of the pronuclear and nucleolar characteristics (zygote-score) has been proposed as an indicator of embryo development and chromosomal complement in human fertilized oocytes [13–19]. The study of human zygote seem to provide important information about embryonic chromosomal arrangements, even if, to date, there is no definitive scientific evidence about its clinical efficacy [17, 18]. Recent data seem to consider pronuclear evaluation as a good criterion when combined with embryo morphology evaluation on Days 2 and 3 , other authors conclude that late parameters (number of blastomeres and embryo grade) have a better prognostic value than zygote score .
In the present study, we have evaluated the clinical significance of zygote-score related to maternal age in patients submitted to ART cycles successfully, obtaining a clinical pregnancy. We observed that all parameters analyzed (pronuclear morphology, nucleolar morphology, polar body alignment and zygote configuration) were generally uniformly distributed in patients ≤32 years old, 33-37 years old and 38-41 years old, showing only few differences related to maternal ages.
Studying the pronuclear morphology, we observed a statistically significant increase in "A" configuration, with a concomitant decrease in "B" configuration, in 38-41 years old in comparison to ≤37 years old patients, both in clinical pregnancies and in ongoing pregnancies/deliveries groups. Due to our unique population characteristics (all patients with clinical pregnancy and maternal age subdivision), it is difficult to compare our results with others present in literature, nevertheless these results appear to corroborate with what has been reported in literature . In agreement with previously reported data , our analysis of nucleolar morphology showed no statistically significant differences in relation to maternal ages, both in clinical pregnancy and in ongoing pregnancy/deliveries groups. This result is in contrast with recently published data showing a correlation between pronuclear morphology and maternal ages . We believe that the discrepancy could be related to the different sample size and to the different maternal age between our patients and those analyzed by Maille and coworkers. Moreover, in contrast with Maille and coworkers, we included in the study population clinical pregnancies obtained both with IVF and ICSI. Again, more recent data seem to confirm the poor clinical significance of nucleolar morphology during embryo selection, reporting no correlations between this parameter and implantation rate .
Finally, studying the last zygote parameter - polar body alignment - related to maternal age, our data showed a statistically significant decrease of "β" configuration in patients 38-41 years old, both in clinical pregnancies and in ongoing pregnancies/deliveries group. We can speculate that polar body alignment, usually evaluated during zygote-score assessment, not appear to have a prognostic value in terms of embryo viability and pregnancy rate. Than, it can not be considered a good tool to select the best embryo to transfer.
This assumption seems to be confirmed by the evaluation of the last parameter considered in our analysis: the whole zygote configuration (pronuclear and nucleolar morphologies plus polar body alignment). In particular, the total absence of statistically significant differences between zygote configurations P1 and P2 grouped by maternal ages, probably provide an additional evidence about the limited importance of zygote-score in assisted reproduction outcomes, as proposed by our previously data and confirmed by most recently published results [18, 19]. Our results showed any statistical significance in term of embryo cleavage and embryo quality related to P1 or P2 configurations both in clinical pregnancies and in ongoing pregnancies/deliveries.