OBJECTIVETo investigate the relationship between human embryo implantation rates and the zygote morphology and establish zygote morphologic indices that indicate the embryo implantation potential after in vitro fertilization and embryo transfer (IVF-ET).

METHODSSixty-two patients with IVF-ET were enrolled in this study, who were below 35 years of age with endometrium thickness no greater than 8 mm on the day of HCG injection. Embryo transfer was performed on day 3 after oocyte retrieval, and 30 patients with successful implantation of all the embryos transferred (implantation rate of 100%) were allocated into the implantation group, and the other 32 patients with implantation failure (implantation rate of 0) served as the control group. The zygote morphologic characteristics were analyzed for the pronuclei, nucleolar precursor bodies (NPB), polar body, cytoplasmic halo, color and granulation of the cytoplasm, and the results were compared between the two groups.

RESULTSThe implantation rate was significantly higher for embryos with the two pronuclei in close vicinity, central position of the pronuclei in the cytoplasm and comparable size of the two pronuclei. Embryos developed from zygotes with linear arrangement of 3 to 7 NPB in moderate sizes tented to have a higher implantation rate (P<0.05). The implantation rate could be obviously lowered when the cytoplasm contained excessive cytoplasmic granularity (P<0.05). The other morphologic characteristics of the embryos such as the polar bodies, color of the cytoplasm, cytoplasm halo, or vacuoles in the cytoplasm did not significantly impact on the implantation rate.

CONCLUSIONThe morphology of the two pronuclei reflects the quality of the zygote and may help predict the developmental potential of the embryo chosen for transfer on day 3 in IVF.