| Objective: (1) Investigate the relationship between implantation rates with embryonic morphologic characteristic during zygote stage, establish zygote morphologic criteria which could indicate the embryo implantation potential after transfer. (2) Study the relationship of day3 embryo quality with implantation rates and filter the valuable factors which can predict development potential of embryos. (3) To establish accumulate embryo scoring system that could predict the outcome of cycles in ART treatment.Methods: This study was carried out at Reproductive Medicine Center of Nanfang Hospital. 166 patients who were treated with ART were investigated prospectively from October 2004 and January 2005. (1) 62 cycle patients were chosen among 166 cycle patients according to age ≤35, the thickness of endometrium ≤8mm and embryo transfer on day3 after oocyte retrieval. 30 cycle patients were classified with implantation group, in this group the implantation rate was 100%, Another 32 cycle patient in coutrol group has implantation rate was 0%. All the zygote morphologic characteristic were analyzed including pronuclei, NPB, polar body, cytoplasmic halo, color and granulation of cytoplasm was investigated respectively. The statistical difference was analyzed between the two groups. (2) The similar comparative methods were adopted in Day3 embryo morphology evaluation between the same two groups, including blastomere quantity, size, position, color, granulation, the ratio andtype of fragments, granular area vacuoles, the thickness and shape of zona pellucida. (3) According to the above studies, eight items with statistical difference were selected to establish four embryo scoring system including zygote, day2 embryo, day3 embryo and day3 embryo combined with zygote. Each of all 381 embryos coming from 166 cycle patients was assessed with four scoring system and the mean scoring was calculated. The first system predict pregnancy outcome by zygote morphology alone. The second one evaluated by day2 embryo morphologic character alone. The third one predict pregnancy outcome by embryo morphology on day3. The last system is a combined score including zygote and embryo morphology on day3, the highest score of this system is 120.Results: (1) It was significant correlativity between embryo implantation and zygote morphology in two pronuclear stage which include pronuclear status, position and size. The implantation rate was significantly higher in those embryos with two close pronuclei, pronuclei located in cytoplasm centre and have equal size. Significant correlation was proved between embryo implantation and morphology characteristic of NPB arranged, position and size. Embryos have a higher implantation rate developed from zygote which NPB have linear arrangement, number between 3 to 7 and middling in size (P<0.05). Implantation rate was obvious decrease when cytoplasm exhibits central granulation (P < 0.05). The other morphologic characteristic of embryos, such as polar bodies, color of cytoplasm, cytoplasmic halo, vacuoles in cytoplasm have no effect on the implantation rate. (2) A statistical difference was observed in the speed of embryo development, blastomere nuclei quantity and the degree of fragmentation between the two groups. 71.4% (40/56) of transferred embryos showed 7~8 cells on day3 in implantation group, especially 8-cell embryos which got a pregnancy rate of 60.7% (34/56). A decrease was observed in control group and the rate was 45.3 % (29/64). In implantation group, 57.1% blastomeres showed at least one visible nucleus and 30.4% embryos have one nucleus in each blastomere. The corresponding rates were 34.4% and 12.5% in control group as well. 41.1% embryos showed fragmentation of Tl pattern inimplantation group, and 15.6% in control group. The implantation rate was same in the two groups when the only difference is the size of blastomeres. The result was the same in fragmentation quantity. The above five morphology indexes of embryo on day3 were analyzed with discriminant analysis method .The results indicated that the number of blastomeres and fragmentation pattern were more important than the size of blastomeres, fragmentation quantity, and a discriminant accordance rate of embryo implantation was 70.0%. It was no statistical difference between other morphologic characters of embryos such as color and granularity of cytoplasma, vacuoles in the cytoplasma, the thickness and shape of zona pellucida with implantation rate. (3) A combined score which day3 linked to zygote was sensitivity. In the statistical analysis, the area under ROC curve was 0.640 that was the biggest one among four scoring systems. The higher the combined score was, the more implantation happened. The clinical pregnancy rate was 50.0% (83/166) and implantation rate was 32.3% (123/381) according to the selective criteria. Embryos with top quality have scores 97—120, embryo obtaining a score 72~96 was good-quality embryo, and a score of poor-quality embryo was less than 72. The highest pregnancy rate was up to 60.6% and implantation rate was 40.8% in the combined scoring system.Conclusion: (1) The morphology of 2PN could reflect the quality of zygote and was an assisted index that could predict the developmental potential of embryo when it was chosen for transfer on day3 in IVF clinic. (2) The blastomere number and fragmentation type were principal factor for embryo selecting in transfer. The best selection among embryo is to choose 8-cell on the day3 after oocyte retrieval. It should pay more attention to the fragmentation type than fragmentation quantity which was considered traditionally before. (3) The combined scoring of day3 and zygote morphology was more predictive value. The combined scoring system could predict accurately the potential for pregnancy and implantation, is a simple and effective, no-traumatic scoring system that assesses numerically embryo quality. It is useful to select embryos effectively in ART clinic.
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