Early pronuclear breakdown is a good indicator of embryo quality and viability

Objective: To examine whether the timing of pronuclear breakdown can be a predictor of embryo quality and viability. Design: Retrospective comparison of the development and quality of early and late developing zygotes. Setting: Infertility and endocrinology unit in a university hospital. Patient(s): One thousand seven hundred eighty-two zygotes obtained in 383 consecutive IVF cycles. Intervention(s): Culture of all fertilized embryos. Main Outcome Measure(S): Number of fertilized zygotes showing early pronuclear breakdown at 22-25 hours postinsemination, embryo quality, pregnancy rates (PR), implantation rates. Result(S): Early pronuclear breakdown embryos had a significantly higher cell number (4.4 +/- 1.2) compared with the late pronuclear breakdown embryos (3.6 +/- 1.4). When comparing the frequency of the early pronuclear breakdown embryos according to the method of fertilization, we failed to find any significant difference between the IVF (37.1%) and the intracytoplasmic sperm injection (ICSI) (41.1%) groups. The transfer of early pronuclear breakdown embryos resulted in a significantly higher clinical pregnancy rate than those with late pronuclear breakdown (48.3% vs. 27.3%). The implantation rate was higher in the early pronuclear breakdown group than in the late pronuclear breakdown group (26.5% vs. 15.1%). Conclusion(s): Early pronuclear breakdown is a strong indicator of embryo viability, and may be used as an additional criterion in the selection of embryos for transfer.