Comparison of Pronuclear Zygote Morphology and Early Cleavage Status of Zygotes As Additional Criteria in the Selection of Day 3 Embryos: a Randomized Study

Objective: Both pronuclear morphology and early zygote cleavage have been used in combination with day 3 criteria to predict implantation and pregnancy. However, in routine practice, it is impractical to use both these criteria to select embryos on day 3. The objective of the present study was to find which of the two criteria is more predictive in terms of implantation and pregnancy.

Design: Randomized study.

Setting: Hospital-based fertility center.

Patient(s): A total of 330 IVF/ICSI patient cycles.

Intervention(s): Patients were randomized to two groups. The embryos of one group were classified into subgroups A, B, and C based on pronuclear morphology (group 1) and the embryos of the second group were classified into subgroups A, B, and C based on early cleavage status (group 2).

Main Outcome Measure(s): Comparisons were made of implantation and pregnancy rates between groups 1 and 2, between subgroups within each group, and between the corresponding subgroups of groups 1 and 2. Progression of zygotes from day 1 to day 3 in group 1 was recorded, and retrospective analysis of pronuclear morphology of zygotes in group 2 was performed.

Result(s): The overall implantation and pregnancy rates tended to be slightly higher for group 1 compared to group 2 patients, but not statistically significant. Further, there was no significant difference between the corresponding subgroups. Implantation and pregnancy rates of subgroup A zygotes from each group were significantly higher (P<.01) than the rates of subgroup C.

Conclusion(s): There was no significant difference between the two groups in terms of implantation and pregnancy. However, pronuclear morphology is a more satisfactory criterion than early cleavage to assist embryo selection on day 3. This is because zygotes with early cleavage ability can be identified from their pronuclear morphology. Thus, observation for early cleavage on day 1 and assessment of progression of embryos on day 2 in addition to pronuclear morphology scoring is not necessary in the selection of embryos for transfer on day 3.