Pronuclear morphology and chromosomal abnormalities as scoring criteria for embryo selection.

OBJECTIVE: To verify whether a correlation exists between pronuclear zygote morphology and the chromosomal condition of preimplantation embryos.
DESIGN: Prospective analysis of pronuclear zygote morphology and preimplantation genetic diagnosis (PGD) for aneuploidy of the resulting embryos.
SETTING: Reproductive medicine unit, day surgery clinic. PATIENT(S): Seventy-seven patients undergoing 107 PGD cycles because of advanced maternal age (77 cycles) or previous IVF failures (30 cycles). INTERVENTION(S): Evaluation of pronuclear zygote morphology and chromosomal condition of the resulting embryos. MAIN OUTCOME MEASURE(S): Rate of embryo development, proportion of euploid embryos, and distribution of chromosomal abnormalities. The position of pronuclei within the ooplasm, the size and distribution of nucleoli, and the orientation of polar bodies with respect to pronuclei were highly predictive for the presence of complex chromosomal abnormalities in the developing embryos; zygotes with juxtaposed pronuclei, large-size nucleoli, and polar bodies with small angles subtended by pronuclei and polar bodies were the configurations associated with the highest rates of euploidy. CONCLUSION(S): The combination of the patterns related to pronuclear zygote morphology indicated four configurations where the proportion of chromosomally normal embryos was significantly higher compared with the other configurations, suggesting the validity of this scoring system for the selection of embryos generated by PGD patients.