The effect of pronuclear morphology on embryo quality parameters and blastocyst transfer outcome

BACKGROUND: Embryo quality may be accurately assessed as early as the pronu clear zygote phase, as shown in recent studies. However, it is not known wh ether good quality zygotes are destined to become good quality cleavage sta ge embryos and blastocysts. METHODS: In this retrospective study, 86 intrac ytoplasmic sperm injection-embryo transfer cycles were studied where each a vailable embryo was scored from the zygote until the blastocyst stage. Embr yonic normality parameters such as pronuclear pattern, early cleavage, clea vage stage embryo grade, the presence of embryos with greater than or equal to8 cells on day 3 and blastocyst quality were recorded. Embryo transfer w as undertaken at the blastocyst stage and the outcome was studied according to the pronuclear pattern exhibited by the zygotes. RESULTS: Embryos that showed an ideal pronuclear pattern (0 PN pattern) cleaved earlier and faste r and resulted in better quality cleavage stage embryos and blastocysts. Th e incidence of blastocyst formation was 72% in zygotes showing a 0 PN patte rn, compared with 12.7% in zygotes with double pronuclear abnormality. High er implantation and pregnancy rates were obtained when at least one blastoc yst derived from a 0 PN pattern zygote was included in the set of embryos t o be transferred. CONCLUSIONS: Our results indicate that the pronuclear pat tern of the zygote is closely related to blastocyst formation and quality. Blastocysts derived from 0 PN zygotes have a higher potential for implantat ion.