Predictive Potential Of Zygote Noninvasive Evaluation

In the late 1990s, it was noted that the timing and regularity of developmental changes in the male and the female pronucleus in human oocytes fertilized in vitro, including pronuclear growth, rotation, and internal differentiation and polarization (Fig. 3), are related to further embryonic development (33-35). Several studies suggested pronuclear zygote scoring systems which were based on the evaluation of the number, size, and

Fertilization Zygote

Figure 3 Micrographs showing the size and distribution of nudeolar precursor body (NPBs) in pronuclei of human zygotes at different phases of pronuclear development. (A) Relatively early phase of pronuclear development, characterized by a high number of NPB in both pronuclei (only part of them is visible at this focal level). The NPBs are relatively small at this phase and are distributed randomly in the pronuclei. (B) Later phase of pronuclear development, characterized by a low number of NPBs in both pronuclei. The NPBs are larger at this phase and show a polarized distribution, with accumulation near that pole of each pronucleus at which this pro-nucleus makes contact with the other one. (Hoffman modulation contrast, original magnification x200.). Source: From Ref. 35.

Figure 3 Micrographs showing the size and distribution of nudeolar precursor body (NPBs) in pronuclei of human zygotes at different phases of pronuclear development. (A) Relatively early phase of pronuclear development, characterized by a high number of NPB in both pronuclei (only part of them is visible at this focal level). The NPBs are relatively small at this phase and are distributed randomly in the pronuclei. (B) Later phase of pronuclear development, characterized by a low number of NPBs in both pronuclei. The NPBs are larger at this phase and show a polarized distribution, with accumulation near that pole of each pronucleus at which this pro-nucleus makes contact with the other one. (Hoffman modulation contrast, original magnification x200.). Source: From Ref. 35.

distribution of NPBs (36). With the exception of one study (37), all other studies agreed that the developmental potential of preimplantation embryos can be predicted by pronuclear evaluation. In concrete terms, pronuclear morphology was reported to predict cleavage speed and cleaving embryo morphology grade (34,35), the risk of developmental arrest during the first 3 days after fertilization (35,38), the risk of blastomere multinucleation (35), the chance of achieving the blastocyst stage in prolonged culture (39,40), and the risk of chromosomal abnormalities (41-43).

From the clinical point of view, these studies made it possible to make decisions about the selection of embryos to be transferred and of those to be cryopreserved for later use as early as the pronuclear zygote stage. Zygote cryopreservation was reported to give excellent outcomes (44), but it was used relatively rarely for fear of not having enough fresh embryos for transfer because of developmental arrest or abnormal development of those embryos that were allowed to cleave. The possibility of prediction of the quality of preimplantation development on the basis of noninvasive zygote evaluation gave a new impetus to zygote cryopreservation. This was particularly important in countries in which cryopreservation of embryos after the first cleavage division was banned by the law, namely in Germany. In fact, several German studies reported satisfactory outcomes of assisted reproduction with embryo selection at the zygote stage with the use of pronuclear assessment criteria (45-47).

These observations have underscored the interest in noninvasive zygote evaluation not only as the only guide for embryo selection, as was the case in Germany, but also as part of a combined sequential evaluations at days 1, 2, and 3 after fertilization (48). With the use of a cumulative scoring system, involving post-fertilization day 1, day 2, and day 3 parameters, the efficacy of day 3 embryo transfer was shown to be comparable to that of day 5 blastocyst transfer (49).

Was this article helpful?

0 0
Pregnancy Guide

Pregnancy Guide

A Beginner's Guide to Healthy Pregnancy. If you suspect, or know, that you are pregnant, we ho pe you have already visited your doctor. Presuming that you have confirmed your suspicions and that this is your first child, or that you wish to take better care of yourself d uring pregnancy than you did during your other pregnancies; you have come to the right place.

Get My Free Ebook


Post a comment